Ok, here's the problem..
I tried to change my screen resolution (from 640x480 to 1280x1024) through the main menu (system settings, display). Linux then tells me to restart the "X server". I rebooted the whole system (which I hope is the same thing as restarting 'X Server'). When I get back, nothing has happend.
I've tried to open the XF86Config file and edit the resolution from there, but nothing stills happend.. when I go back to the edited file, after rebooting the computer, the values have been restored as they were from the beginning.. I know that my graphich card supports the higher resolution, and so does my monitor. The graphic card is identified by Linux, but not my monitor if that could be the problem?
Im running Red Hat 9 by the way

Thanks

Try changing the "modes" lines at the bottom of /etc/X11/XF86Config using gedit as root user.

ie

SubSection "Display"
Depth 16
Modes "1280x1024" "800x600" "640x480"
EndSubSection

So that the first entry in all the sections is

"1280x1024"

and save the file, then reboot

I've done as you said, but it still wont change..
my config file looks like this at the moment:
Section "Monitor"
Identifier "Monitor0"
VendorName "Monitor Vendor"
ModelName "Unprobed Monitor"
HorizSync 31.5 - 37.9
VertRefresh 50.0 - 70.0
Option "dpms"
EndSection

Section "Device"
Identifier "Videocard0"
Driver "nv"
VendorName "Videocard vendor"
BoardName "NVIDIA GeForce 4 (generic)"
EndSection

Section "Screen"
Identifier "Screen0"
Device "Videocard0"
Monitor "Monitor0"
DefaultDepth 24
SubSection "Display"
Depth 24
Modes "1280x1024" "800x600" "640x480"
EndSubSection
EndSection

Looks like it _should_ startup in 1280 resolution?

I've checked the display settings in the main menu (system settings), and it says that it should be 1280 resoultion.. but it isn't! What could be wrong?

Thanks

Yes.
Your monitor is set to Unprobed Monitor, so you will not be able to set the resolution higher than 800x600.

To set your monitor, you can use the RH9 GUI.
In the menu, System Settings -> Display
or at the command line, type: redhat-config-xfree86

Click on the Advanced tab.

my monitor is not in the list! Its a LG Flatron F900B .. suggestions?