Alter your /etc/X11/xorg.conf - find the line(s) that describe the resolutions (look for 1024x768 and you'll find the line(s) you need) and add in front of the resolution list at that line your desired resolution - after you've made sure your screen and gfx card support it. If there are multiple resolutions on the line (separated by space), the first one is used and if it's unavailable/can't be used, then the next etc.
There might also be multiple lines that contain resolutions - one for each color depth for example. Then simply edit the one you need or them all..save and restart X (ctrl+alt+backspace) to see if it worked.
EDIT: at some cases you're able to change the resolution with ctrl+alt++ (plus) and ctrl+alt+- (minus) if you have multiple resolutions configured.
Last edited by b0uncer; 08-09-2006 at 08:48 AM.