The graphic card is identified by Linux, but not my monitor if that could be the problem?
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.