krinha,

Eu, quando a distribuição não detecta a placa e monitor corretamente, coloco pra placa de video "vesa" e monitor "generic Super VGA"... Segue um exemplo do XF86cfg-4 que tenho em Debian, na parte "Modes" vc pode colocar "1024x768" "800x600" "640x320":

Section "Device"
Identifier "generec Vesa"
Driver "vesa"
EndSection

Section "Monitor"
Identifier "Monitor Genérico"
HorizSync 28-49
VertRefresh 43-72
Option "DPMS"
EndSection

Section "Screen"
Identifier "Default Screen"
Device "vesa"
Monitor "Monitor Genérico"
DefaultDepth 24
SubSection "Display"
Depth 1
Modes "1024x768"
EndSubSection
SubSection "Display"
Depth 4
Modes "1024x768"
EndSubSection
SubSection "Display"
Depth 8
Modes "1024x768"
EndSubSection
SubSection "Display"
Depth 15
Modes "1024x768"
EndSubSection
SubSection "Display"
Depth 16
Modes "1024x768"
EndSubSection
SubSection "Display"
Depth 24
Modes "1024x768"
EndSubSection
EndSection

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

[]s,
Everton.