I have an old video card (Diamond Speedstar 24x) which isn't supported by xfree 4, so i compiled xfree 3.3.6 from source. I ran the included xf86config program to create my XF86Config file, but whenever I run "startx," I get an error message which says "Fatal server error: No screens found"
Here is an extract from the "Screens" section of my config file.

# **********************************************************************
# Screen sections
# **********************************************************************

# The Colour SVGA server

Section "Screen"
Driver "svga"
# Use Device "Generic VGA" for Standard VGA 320x200x256
#Device "Generic VGA"
Device "My Video Card"
Monitor "Monitor"
Subsection "Display"
Depth 8
# Omit the Modes line for the "Generic VGA" device
Modes "1024x768" "800x600" "640x480"
ViewPort 0 0
# Use Virtual 320 200 for Generic VGA
EndSubsection
Subsection "Display"
Depth 16
Modes "1024x768" "800x600" "640x480"
ViewPort 0 0
EndSubsection
Subsection "Display"
Depth 24
Modes "640x480"
ViewPort 0 0
EndSubsection
Subsection "Display"
Depth 32
Modes "640x400"
ViewPort 0 0
EndSubsection
EndSection

# The 16-color VGA server

Section "Screen"
Driver "vga16"
Device "Generic VGA"
Monitor "Monitor"
Subsection "Display"
Modes "640x480" "800x600"
ViewPort 0 0
Virtual 800 600
EndSubsection
EndSection

# The Mono server

Section "Screen"
Driver "vga2"
Device "Generic VGA"
Monitor "Monitor"
Subsection "Display"
Modes "640x480" "800x600"
ViewPort 0 0
Virtual 800 600
EndSubsection
EndSection

try to run xfree86setup
your XF86Config shows that you have loaded the default settings for a generic VGA card
this xfree86setup try to detect the chipset...
can work better..
i hope... ; )

i had the same problem when i set my depth to 24,

try setting your card to vga, and your depth to something lower, say 16.. that might do the job

HTH