Screen resolution question

[Andres Gonzalez]

I recently install the new Ubuntu on a new box I just built. I had an 
old monitor and used it not really knowing its capabilities. After 
Ubuntu was installed, my default screen resolution is 640x480. If I go 
into <System><Preferences><Screen Resolution> the only option I am given 
is 640x480. So, I figured that the old monitor I was using only 
supported up to 640x480 resolution and that Ubuntu was using the highest 
available resolution. Then I booted up off the CD and the screen 
resolution was 1280x1024. Now I know that the monitor indeed supports 
this higher resolution.

How do I change my default settings to the higher screen resolution? I 
am NOT given the option in the <System><Preferences><Screen Resolution> 
dialog so I must change it elsewhere.

Thanks,

-Andres