here...try this...it'll tell you all you need to know so you can give us the right numbers... www.belarc.com ...just click free download and look through it and then tell us what you got bro.
I think the best card for those specs and not too expensive would be the Nvidia GeForce 5700 Ultra (about 175$) or the Radeon 9800 Pro (about 220$) i heard the 5900 series has problems with the drivers but have no proof to back that up... anyway good hunting. btw www.newegg.com has very reasonable prices and fast shipping.
Macattack, you play EQ? I feel sorry for you already... very addictive, can ruin your life fast.
Anyways, you can find out what kind of VGA slot you have by using CPU-Z, it is in my signature below. There is a section called "AGP" under the "Mainboard" tab, it will either say "4x" or "8x".