I'm running an install of CentOS 5.5 virtually and for some reason I only have 2 available screen resolutions - 800x600 and 640x480. Does anybody know how I can add some bigger resolutions?

I've had a look in /etc/X11/xorg.conf and it is knows that the graphics card is virtual, but even listing the resolutions that I want fails.

Here is the default screen section -

Secton "Screen"
        Identifiew "Screen0"
        Device     "Videocard0"
        DefaultDepth    24
        SubSection "Display"
                Viewport 0 0
                Depth    24
        EndSubSection
EndSection

And here is what I tried adding to SubSection "Display" -

Mode "1024x768" "1280x1024"