Hi Tom,
please try the following:
replace your monitor section with this one:
Section "Monitor" Identifier "Monitor0" VendorName "Monitor Vendor" ModelName "Unknown monitor" HorizSync 31.5 - 48.5 VertRefresh 40.0 - 70.0 EndSection
And your Screen section with this one:
Section "Screen" Identifier "Screen0" Device "Videocard0" Monitor "Monitor0" DefaultDepth 24 SubSection "Display" Viewport 0 0 Depth 16 Modes "1024x768" EndSubSection SubSection "Display" Viewport 0 0 Depth 24 Modes "1024x768" EndSubSection EndSection
-volker