This doesnt happen under XP, so its unlikely to be a faulty card.
lspci says the card is a ATI Technologies Inc RS480 [Radeon Xpress 200G Series].
Does the output below suggest anything that needs reconfiguring ?
user:$ cat /etc/X11/xorg.conf
Section "ServerLayout"
Identifier "X.org Configured"
Screen 0 "Screen0" 0 0
InputDevice "Mouse0" "CorePointer"
InputDevice "Keyboard0" "CoreKeyboard"
EndSection
Section "Files"
RgbPath "/usr/share/X11/rgb"
ModulePath "/usr/lib/xorg/modules"
FontPath "/usr/share/fonts/TTF"
FontPath "/usr/share/fonts/OTF"
FontPath "/usr/share/fonts/Type1"
FontPath "/usr/share/fonts/misc"
FontPath "/usr/share/fonts/75dpi/:unscaled"
EndSection
Section "Module"
Load "glx"
Load "extmod"
Load "xtrap"
Load "record"
Load "GLcore"
Load "dbe"
Load "dri"
Load "freetype"
Load "type1"
EndSection
!keyboard, mouse sections not shown
Section "Monitor"
DisplaySize 269 201 # 96 DPI @ 1024x768
Option "UseEdidFreqs" "1"
#DisplaySize 370 300 # mm
Identifier "Monitor0"
VendorName "ACR"
ModelName "Acer AL1911"
### Comment all HorizSync and VertRefresh values to use DDC:
HorizSync 24.0 - 80.0
VertRefresh 56.0 - 75.0
Option "DPMS"
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>]
Identifier "Card0"
Driver "fglrx"
VendorName "ATI Technologies Inc"
BoardName "RS480 [Radeon Xpress 200G Series]"
BusID "PCI:1:5:0"
EndSection
Section "Screen"
Identifier "Screen0"
Device "Card0"
Monitor "Monitor0"
DefaultDepth 24
SubSection "Display"
Viewport 0 0
Depth 1
Modes "1024x768" "800x600" "640x480"
EndSubSection
SubSection "Display"
Viewport 0 0
Depth 4
Modes "1024x768" "800x600" "640x480"
EndSubSection
SubSection "Display"
Viewport 0 0
Depth 8
Modes "1024x768" "800x600" "640x480"
EndSubSection
SubSection "Display"
Viewport 0 0
Depth 15
Modes "1024x768" "800x600" "640x480"
EndSubSection
SubSection "Display"
Viewport 0 0
Depth 16
Modes "1024x768" "800x600" "640x480"
EndSubSection
SubSection "Display"
Viewport 0 0
Depth 24
Modes "1024x768" "800x600" "640x480"
EndSubSection
EndSection
Section "DRI"
Mode 0666
EndSection
Section "Extensions"
Option "Composite" "on"
EndSection