[R600 HD 2600] R600/R700 does not support composite - "Desktop effects could not be enabled"

[Problem]
As can be seen at http://wiki.x.org/wiki/RadeonFeature, 3D support that compiz requires is listed as a work-in-progress for R600/R700 class chips. It requires a mesa driver to support this family of chips, which is on the todo list upstream but won't be available for Jaunty.

Render-based compositers (like metacity) should work fine, at least as of 6.11.0.

[Original Report]
I am using the Intrepid Ibex prerelease (fully up to date as at 7 Oct 2008). My laptop is a Gateway M-Series, with a Core 2 Duo...and an ATI Mobility Radeon HD 2600 graphics card.

When I attempt to enable desktop effects, I get a message that "Desktop effects could not be enabled."

[lspci]
00:00.0 Host bridge [0600]: Intel Corporation Mobile PM965/GM965/GL960 Memory Controller Hub [8086:2a00] (rev 03)
01:00.0 VGA compatible controller [0300]: ATI Technologies Inc M76 [Radeon Mobility HD 2600 Series] [1002:9581]
 Subsystem: Gateway 2000 Device [107b:0562]

My xorg.conf file follows:
Section "ServerLayout"
 Identifier "X.org Configured"
 Screen 0 "Screen0" 0 0
 InputDevice "Mouse0" "CorePointer"
 InputDevice "Keyboard0" "CoreKeyboard"
EndSection

Section "Files"
 ModulePath "/usr/lib/xorg/modules"
 FontPath "/usr/share/fonts/X11/misc"
 FontPath "/usr/share/fonts/X11/cyrillic"
 FontPath "/usr/share/fonts/X11/100dpi/:unscaled"
 FontPath "/usr/share/fonts/X11/75dpi/:unscaled"
 FontPath "/usr/share/fonts/X11/Type1"
 FontPath "/usr/share/fonts/X11/100dpi"
 FontPath "/usr/share/fonts/X11/75dpi"
 FontPath "/var/lib/defoma/x-ttcidfont-conf.d/dirs/TrueType"
EndSection

Section "Module"
 Load "glx"
 Load "xtrap"
 Load "dbe"
 Load "dri"
 Load "extmod"
 Load "record"
EndSection

Section "InputDevice"
 Identifier "Keyboard0"
 Driver "kbd"
EndSection

Section "InputDevice"
 Identifier "Mouse0"
 Driver "mouse"
 Option "Protocol" "auto"
 Option "Device" "/dev/input/mice"
 Option "ZAxisMapping" "4 5 6 7"
EndSection

Section "Monitor"
 Identifier "Monitor0"
 VendorName "Monitor Vendor"
 ModelName "Monitor Model"
EndSection

Section "Device"
        ### Available Driver options are:-
        ### Values: <i>: integer, <f>: float, <bool>: "True"/"False",
        ### <string>: "String", <freq>: "<f> Hz/kHz/MHz"
        ### [arg]: arg optional
        #Option "NoAccel" # [<bool>]
        #Option "SWcursor" # [<bool>]
        #Option "Dac6Bit" # [<bool>]
        #Option "Dac8Bit" # [<bool>]
        #Option "BusType" # [<str>]
        #Option "CPPIOMode" # [<bool>]
        #Option "CPusecTimeout" # <i>
        #Option "AGPMode" # <i>
        #Option "AGPFastWrite" # [<bool>]
        #Option "AGPSize" # <i>
        #Option "GARTSize" # <i>
        #Option "RingSize" # <i>
        #Option "BufferSize" # <i>
        #Option "EnableDepthMoves" # [<bool>]
        #Option "EnablePageFlip" # [<bool>]
        #Option "NoBackBuffer" # [<bool>]
        #Option "DMAForXv" # [<bool>]
        #Option "FBTexPercent" # <i>
        #Option "DepthBits" # <i>
        #Option "PCIAPERSize" # <i>
        #Option "AccelDFS" # [<bool>]
        #Option "DDCMode" # [<bool>]
        #Option "IgnoreEDID" # [<bool>]
        #Option "DisplayPriority" # [<str>]
        #Option "PanelSize" # [<str>]
        #Option "ForceMinDotClock" # <freq>
        #Option "ColorTiling" # [<bool>]
        #Option "VideoKey" # <i>
        #Option "RageTheatreCrystal" # <i>
        #Option "RageTheatreTunerPort" # <i>
        #Option "RageTheatreCompositePort" # <i>
        #Option "RageTheatreSVideoPort" # <i>
        #Option "TunerType" # <i>
        #Option "RageTheatreMicrocPath" # <str>
        #Option "RageTheatreMicrocType" # <str>
        #Option "ScalerWidth" # <i>
        #Option "RenderAccel" # [<bool>]
        #Option "SubPixelOrder" # [<str>]
        #Option "ShowCache" # [<bool>]
        #Option "DynamicClocks" # [<bool>]
        #Option "VGAAccess" # [<bool>]
        #Option "ReverseDDC" # [<bool>]
        #Option "LVDSProbePLL" # [<bool>]
        #Option "AccelMethod" # <str>
        #Option "DRI" # [<bool>]
        #Option "ConnectorTable" # <str>
        #Option "DefaultConnectorTable" # [<bool>]
        #Option "DefaultTMDSPLL" # [<bool>]
        #Option "TVDACLoadDetect" # [<bool>]
        #Option "ForceTVOut" # [<bool>]
        #Option "TVStandard" # <str>
        #Option "IgnoreLidStatus" # [<bool>]
        #Option "DefaultTVDACAdj" # [<bool>]
        #Option "Int10" # [<bool>]
 Identifier "Card0"
 Driver "radeon"
 VendorName "ATI Technologies Inc"
 BoardName "M76 [Radeon Mobility HD 2600 Series]"
 BusID "PCI:1:0:0"
EndSection

Section "Screen"
 Identifier "Screen0"
 Device "Card0"
 Monitor "Monitor0"
 SubSection "Display"
  Viewport 0 0
  Depth 1
 EndSubSection
 SubSection "Display"
  Viewport 0 0
  Depth 4
 EndSubSection
 SubSection "Display"
  Viewport 0 0
  Depth 8
 EndSubSection
 SubSection "Display"
  Viewport 0 0
  Depth 15
 EndSubSection
 SubSection "Display"
  Viewport 0 0
  Depth 16
 EndSubSection
 SubSection "Display"
  Viewport 0 0
  Depth 24
 EndSubSection
EndSection