Graphics recommendation

Hey guys, I have custom built PC by me and it's got an M2-AN ABIT motherboard with 2.5gb of ram. I have a Dual Core AMD Athlon 5000+ Black Edition that I have overclocked from 2.6ghz to 3.2ghz with a stable condition on Windows XP 32-bit. Now, my question is, with this type of CPU and ram what would be a good recommendation for a somewhat cheap graphics card but does a better job than what I already have, preferably a Nvidia g-card. I currently have an 8600GT ASUS that has been overclocked by 33% of it's original power, making it run at approximately 600mhz core clock and 700 mhz memory clock. I am looking to spend hopefully right around $100 if it is possible, if not, what would be the next best deal?

This card is a little slower than the GTS 250, but under $100 w/o rebate and comes with a lifetime warranty.