Is someone succeded to activate composite option in KDE4 ? I have tried but I
always get an error in my .xsession-errors log file.

This is what I get in my .xsession-errors file (I have cut uneeded messages):

kwin(22590) KWin::Extensions::init: Extensions: shape: 0x "11"
composite:0x"4" render: 0x "a" fixes: 0x "40"
kwin(22590) KWin::CompositingPrefs::detect: glx version is 1 . 4
kwin(22590) KWin::CompositingPrefs::detectDriverAndVersion: GL vendor is
"NVIDIA Corporation"
kwin(22590) KWin::CompositingPrefs::detectDriverAndVersion: GL renderer is
"GeForce 6200/AGP/SSE2"
kwin(22590) KWin::CompositingPrefs::detectDriverAndVersion: GL version is "1.4
(2.1.2 NVIDIA 173.14.05)"
kwin(22590) KWin::CompositingPrefs::detectDriverAndVersion: XGL: no
kwin(22590) KWin::CompositingPrefs::detectDriverAndVersion: Detected driver
"nvidia" , version "173.14.05.)"
kwin(22590) KWin::CompositingPrefs::applyDriverSpecificOptions: nvidia >=
96.39, enabling compositing
kwin(22590) KDecorationPlugins::loadPlugin: kwin : path
"/usr/lib/kde4/kwin3_ozone.so" for "kwin3_ozone"
kwin(22590) KWin::Extensions::init: Extensions: shape: 0x "11" composite: 0x
"4" render: 0x "a" fixes: 0x "40"
kwin(22590) KWin::Extensions::init: Extensions: shape: 0x "11" composite: 0x
"4" render: 0x "a" fixes: 0x "40"
kwin(22590) KWin::Workspace::setupCompositing: OpenGL compositing
kwin(22590) KWin::SceneOpenGL::initBufferConfigs: Drawable visual (depth 24
): 0x "59"
kwin(22590) KWin::SceneOpenGL::initBufferConfigs: Drawable visual (depth 32
): 0x "80"
kwin(22590) KWin::SceneOpenGL::initBuffer: Buffer visual (depth 24 ): 0x "57"
kwin(22590) KWin::SceneOpenGL::SceneOpenGL: DB: true , TFP: true , SHM: false
, Direct: false
kwin(22590) KWin::Workspace::setupCompositing: Refresh rate 60 Hz
kwin(22590)/kio (KSycoca) KSycocaPrivate::openDatabase: Trying to open ksycoca
from "/var/tmp/kdecache-fred/ksycoca4"
kwin(22590) KWin::EffectsHandlerImpl::loadEffect: Trying to load
"kwin4_effect_sharpen"
kwin(22590) KWin::EffectsHandlerImpl::loadEffect: EffectsHandler::loadEffect :
Effect "kwin4_effect_sharpen" is not supported
kwin(22590) KWin::EffectsHandlerImpl::loadEffect: Trying to load
"kwin4_effect_blur"
kwin(22590) KWin::EffectsHandlerImpl::loadEffect: EffectsHandler::loadEffect :
Effect "kwin4_effect_blur" is not supported
kwin(22590) KWin::EffectsHandlerImpl::loadEffect: Trying to load
"kwin4_effect_coverswitch"
kwin(22590) KWin::EffectsHandlerImpl::loadEffect: Trying to load
"kwin4_effect_desktopgrid"
kded(22580) Kded::loadModule: Successfully loaded module "kdedglobalaccel"
kwin(22590) KWin::EffectsHandlerImpl::loadEffect: Trying to load
"kwin4_effect_maketransparent"
kwin(22590) KWin::EffectsHandlerImpl::loadEffect: Trying to load
"kwin4_effect_taskbarthumbnail"
kwin(22590) KWin::EffectsHandlerImpl::loadEffect: Trying to load
"kwin4_effect_minimizeanimation"
kwin(22590) KWin::EffectsHandlerImpl::loadEffect: Trying to load
"kwin4_effect_dialogparent"
kwin(22590) KWin::EffectsHandlerImpl::loadEffect: Trying to load
"kwin4_effect_zoom"
kwin(22590) KWin::EffectsHandlerImpl::loadEffect: Trying to load
"kwin4_effect_presentwindows"
kwin(22590) KWin::EffectsHandlerImpl::loadEffect: Trying to load
"kwin4_effect_scalein"
kwin(22590) KWin::EffectsHandlerImpl::loadEffect: Trying to load
"kwin4_effect_shadow"
kwin(22590) KWin::EffectsHandlerImpl::loadEffect: Trying to load
"kwin4_effect_dimscreen"
kwin(22590) KWin::EffectsHandlerImpl::loadEffect: Trying to load
"kwin4_effect_wobblywindows"
kwin(22590) KWin::EffectsHandlerImpl::loadEffect: Trying to load
"kwin4_effect_fade"
kwin(22590) KWin::EffectsHandlerImpl::loadEffect: Trying to load
"kwin4_effect_flipswitch"
kwin(22590) KWin::EffectsHandlerImpl::loadEffect: Trying to load
"kwin4_effect_boxswitch"
kwin(22590) KWin::EffectsHandlerImpl::loadEffect: Trying to load
"kwin4_effect_logout"
kwin(22590) KWin::EffectsHandlerImpl::loadEffect: Trying to load
"kwin4_effect_login"
kwin(22590) KWin::EffectsHandlerImpl::unloadEffect:
EffectsHandler::unloadEffect : Unloading Effect : "kwin4_effect_dimscreen"
kwin(22590) KWin::EffectsHandlerImpl::unloadEffect:
EffectsHandler::unloadEffect : Unloading Effect : "kwin4_effect_zoom"
kwin(22590) KWin::EffectsHandlerImpl::unloadEffect:
EffectsHandler::unloadEffect : Unloading Effect :
"kwin4_effect_taskbarthumbnail"
kwin(22590) KWin::EffectsHandlerImpl::unloadEffect:
EffectsHandler::unloadEffect : Unloading Effect : "kwin4_effect_login"
kwin(22590) KWin::EffectsHandlerImpl::unloadEffect:
EffectsHandler::unloadEffect : Unloading Effect : "kwin4_effect_logout"
kwin(22590) KWin::EffectsHandlerImpl::unloadEffect:
EffectsHandler::unloadEffect : Unloading Effect :
"kwin4_effect_wobblywindows"
kwin(22590) KWin::EffectsHandlerImpl::unloadEffect:
EffectsHandler::unloadEffect : Unloading Effect : "kwin4_effect_boxswitch"
kwin(22590) KWin::EffectsHandlerImpl::unloadEffect:
EffectsHandler::unloadEffect : Unloading Effect : "kwin4_effect_flipswitch"
kwin(22590) KWin::EffectsHandlerImpl::unloadEffect:
EffectsHandler::unloadEffect : Unloading Effect : "kwin4_effect_scalein"
kwin(22590) KWin::EffectsHandlerImpl::unloadEffect:
EffectsHandler::unloadEffect : Unloading Effect :
"kwin4_effect_minimizeanimation"
kwin(22590) KWin::EffectsHandlerImpl::unloadEffect:
EffectsHandler::unloadEffect : Unloading Effect :
"kwin4_effect_maketransparent"
kwin(22590) KWin::EffectsHandlerImpl::unloadEffect:
EffectsHandler::unloadEffect : Unloading Effect : "kwin4_effect_desktopgrid"
kwin(22590) KWin::EffectsHandlerImpl::unloadEffect:
EffectsHandler::unloadEffect : Unloading Effect : "kwin4_effect_coverswitch"
kwin(22590) KWin::EffectsHandlerImpl::unloadEffect:
EffectsHandler::unloadEffect : Unloading Effect : "kwin4_effect_fade"
kwin(22590) KWin::EffectsHandlerImpl::unloadEffect:
EffectsHandler::unloadEffect : Unloading Effect :
"kwin4_effect_presentwindows"
kwin(22590) KWin::EffectsHandlerImpl::unloadEffect:
EffectsHandler::unloadEffect : Unloading Effect : "kwin4_effect_dialogparent"
kwin(22590) KWin::EffectsHandlerImpl::unloadEffect:
EffectsHandler::unloadEffect : Unloading Effect : "kwin4_effect_shadow"
kwin: X Error (error: BadLength [16], request: X_GLXDestroyWindow[GLX+32],
resource: 0x1a6)
<unknown program name>(22591)/ checkComposite: Plasma has an argb visual
0x82544e0 31457281
<unknown program name>(22591)/ checkComposite: Plasma is COMPOSITE-less on
0x824c598
plasma(22593)/kdesktop PlasmaApp::PlasmaApp: Setting the pixmap cache size to
10349 kilobytes
kwin(22590) KWin::Extensions::init: Extensions: shape: 0x "11" composite: 0x
"4" render: 0x "a" fixes: 0x "40"
kwin(22590) KWin::Workspace::setupCompositing: OpenGL compositing
kwin(22590): Couldn't find framebuffer configuration for default depth!
kwin(22590): Failed to initialize compositing, compositing disabled
kwin(22590): Consult http://techbase.kde.org/Projects/KWin/4.0-release-
notes#Setting_up

my lspci output:

00:00.0 Host bridge: Intel Corporation 82865G/PE/P DRAM Controller/Host-Hub
Interface (rev 02)
00:01.0 PCI bridge: Intel Corporation 82865G/PE/P PCI to AGP Controller (rev
02)
00:1d.0 USB Controller: Intel Corporation 82801EB/ER (ICH5/ICH5R) USB UHCI
Controller #1 (rev 02)
00:1d.1 USB Controller: Intel Corporation 82801EB/ER (ICH5/ICH5R) USB UHCI
Controller #2 (rev 02)
00:1d.2 USB Controller: Intel Corporation 82801EB/ER (ICH5/ICH5R) USB UHCI
Controller #3 (rev 02)
00:1d.3 USB Controller: Intel Corporation 82801EB/ER (ICH5/ICH5R) USB UHCI
Controller #4 (rev 02)
00:1d.7 USB Controller: Intel Corporation 82801EB/ER (ICH5/ICH5R) USB2 EHCI
Controller (rev 02)
00:1e.0 PCI bridge: Intel Corporation 82801 PCI Bridge (rev c2)
00:1f.0 ISA bridge: Intel Corporation 82801EB/ER (ICH5/ICH5R) LPC Interface
Bridge (rev 02)
00:1f.1 IDE interface: Intel Corporation 82801EB/ER (ICH5/ICH5R) IDE
Controller (rev 02)
00:1f.2 IDE interface: Intel Corporation 82801EB (ICH5) SATA Controller (rev
02)
00:1f.3 SMBus: Intel Corporation 82801EB/ER (ICH5/ICH5R) SMBus Controller (rev
02)
00:1f.5 Multimedia audio controller: Intel Corporation 82801EB/ER (ICH5/ICH5R)
AC'97 Audio Controller (rev 02)
01:00.0 VGA compatible controller: nVidia Corporation NV44A [GeForce 6200]
(rev a1)
02:01.0 FireWire (IEEE 1394): Texas Instruments TSB43AB23 IEEE-1394a-2000
Controller (PHY/Link)
02:02.0 Ethernet controller: Realtek Semiconductor Co., Ltd.
RTL-8139/8139C/8139C+ (rev 10)

Extract of my xorg.conf:
...
Section "Device"
  Identifier "device1"
  VendorName "nVidia Corporation"
  BoardName "NVIDIA GeForce FX and later"
  Driver "nvidia"                
  Option "AddARGBVisuals" "true"      
  Option "AddARGBGLXVisuals" "true"    
  Option "DynamicTwinView" "false"    
  Option "RenderAccel" "true"        
  Option "AllowGLXWithComposite" "true"
EndSection
...
Section "Extensions"
  Option "Composite" "Enable"
  Option "RENDER" "true"  
  Option "DAMAGE" "true"  
EndSection


There is no error in my /var/log/Xorg.0.log file.