|"How can I remove old ATi drivers and go back to the standard VGA driver from Microsoft?"|
Why would you want to do that? Graphics performance will drop off even more with standard VGA.
"I have downloaded the "newest" drivers from the AMD website but I have been unable to install them"
I can only guess that you got the wrong drivers. The Rage Pro is very old & is no longer supported. You need to get the older legacy drivers. You're not running XP on that old system, are you? Does it have at least 512MB RAM? If not, it's gonna perform poorly no matter what you do.
For 9x, get driver version 4.13.2655
For XP, get driver version 5.10.2600.6010