problema configurazione compiz

[z3ro <z3ro.2@tele2.it>]

Car* tutt*,

sono letteralmente nelle vostre mani.
ho appena installato compiz su una lenny con scheda grafica ati x850xt, 
driver radeon, xorg 7.1, seguendo la guida di debianizzati.org

digitando al riavvio: $ compiz --replace gconf mi restituisce il 
seguente errore:

Checking for Xgl: not present.
Detected PCI ID for VGA: 06:00.0 0300: 1002:5d52 (prog-if 00 [VGA 
controller])
Checking for texture_from_pixmap: present.
Checking for non power of two support: present.
Checking for Composite extension: present.
Comparing resolution (1280x1024) to maximum 3D texture size (2048): Passed.
Checking for nVidia: not present.
Checking for FBConfig: present.
Checking for Xgl: not present.
Starting gtk-window-decorator
/usr/bin/compiz.real (core) - Fatal: No GLXFBConfig for default depth, 
this isn't going to work.
/usr/bin/compiz.real (core) - Error: Failed to manage screen: 0
/usr/bin/compiz.real (core) - Fatal: No manageable screens found on 
display :0.0

che fare? vi ringrazio anticipatamente

vi allego la configurazione di xorg:

Section "Files"
EndSection

Section "InputDevice"
        Identifier "Generic Keyboard"
        Driver "kbd"
        Option "CoreKeyboard"
        Option "XkbRules" "xorg"
        Option "XkbModel" "pc105"
        Option "XkbLayout" "it"
EndSection

Section "InputDevice"
        Identifier "Configured Mouse"
        Driver "mouse"
        Option "CorePointer"
        Option "Device" "/dev/input/mice"
        Option "Protocol" "ImPS/2"
        Option "Emulate3Buttons" "true"
EndSection

Section "Device"
        Identifier "ATI Technologies Inc R480 [Radeon X850XT (PCIE)] 
(Primary)"
        Driver "radeon"
        BusID "PCI:6:0:0"
        Option "AccelMethod" "XAA"
        Option "XAANoOffscreenPixmaps" "true"
        Option "AddARGBGLXVisuals" "true"
        Option "AllowGLXWithComposite" "true"
EndSection

Section "Monitor"
        Identifier "Monitor Generico"
        Option "DPMS"
        HorizSync 28-64
        VertRefresh 43-60
EndSection

Section "Screen"
        Identifier "Default Screen"
        Device "ATI Technologies Inc R480 [Radeon X850XT (PCIE)] (Primary)"
        Monitor "Monitor Generico"
        DefaultDepth 24
        SubSection "Display"
                Modes "1280x1024"
        EndSubSection
EndSection

Section "ServerLayout"
        Identifier "Default Layout"
        Screen "Default Screen"
        InputDevice "Generic Keyboard"
        InputDevice "Configured Mouse"
        Option "AIGLX" "true"
EndSection

Section "Extensions"
    Option "Composite" "Enable"
    Option "RENDER" "true"
    Option "DAMAGE" "true"
EndSection

--
in girum imus nocte et consumimur igni