ATI 3D Rage Pro AGP 1X / 2X (RE Post)

[WP]

First let me say that I am a new, and I mean new....Linux user so I have no
experience whatever with using this operating
system.  I am trying to get a Linux box ready to use EMC in my machine shop.
I have an old  Dell Optiplex GX1 that has a Pentium III 500 processor and
448 mg of ram. It has an on board ATI 3D Rage ProAGP 1x/2x graphics card. 
I am using this with a 15" Dell flat pannel monitor.
I installed Ubuntu 6.06 from CD that was sent from Ubuntu. The problem
that I am having is that the only resolution that is available for the
monitor is 640 x 480 and I know that this card and monitor should run at higher
resolutions than this.
Please remember in your responses that I know nothing about using
Linux....so try to make any suggestions as simple and clear as possible.
Thank you in advance for any assistance...