Virtual desktop

[Hans <hansfong@zonnet.nl>]

I configured my /etc/XF86Config with three modelines (640x480, 800x600 and
1024x768) and the rest like this...

Section "Screen"
   Driver          "SVGA"
   Device          "Primary Card"
   Monitor         "Primary Monitor"
   DefaultColorDepth 16
   BlankTime       0
   SuspendTime     0
   OffTime         0
   SubSection "Display"
      Depth        8
      Modes        "800x600" "640x480" "1024x768"
   EndSubSection

...and so on.

When I start X it comes up 800x600 in 16kbit color depth. Great. However
the virtual desktop seems to be 1024x768. I could add the line "Virtual
800 600" but then I lose my 1024x768 mode and I still have a 800x600
virtual desktop when in 640x480 mode. Not great.

What I want is for the virtual desktop to be the same as the resolution I
am in, so that when I cycle through the modes with Ctrl-Alt-KP+ it adjusts.
Is that possible and would someone be so nice to post the recipe? 

Related question: is there a program/script that can calculate modelines
for odd resolutions (I need 786x584). XF86Setup can't do this mode and I
couldn't figure out how to do it with xvidtune. TIA

--hans