It's an AMD Athlon 64. Those Radeon models were kinda what I was looking at. Or a Geforce 7600 GS. I saw somewhere though where it was stated that the HD 3850 may not take full advantage of a single core processor and a better alternative might be a 2600 XT. All of these are pretty tough to find for purchase, and the few I've seen are more expensive than pci-e cards that more than double their performance Might just be time to upgrade the entire thing.
The best agp card is the hd 3850, http://www.tomshardware.com/reviews/ati-agp-3850-agp,19... I highly recommend upgrading the entire rig to pci-e. I did the exact thing as you and now Im stuck with a okay computer that in the end I spent 500$ on. My original specs were 3.0 ghz p4, 1.5 gb ddr ram, hd 3850 agp, and 120 gb hd 7200 rpm. I could run call of duty 4 on medium . Things went bad after my mobo and Hd burned out from my new high watt psu I bought to power my new card. I then had to buy all new parts. Long story short, upgrading to pci-e isn't all that bad or expensive, just do it in parts if you have to. Also I would go with sapphire, most have better cooling and clock speeds and they are more reliable than powercolor.
I saw somewhere though where it was stated that the HD 3850 may not take full advantage of a single core processor and a better alternative might be a 2600 XT. All of these are pretty tough to find for purchase, and the few I've seen are more expensive than pci-e cards that more than double their performance Might just be time to upgrade the entire thing.
Its the other way around. The 3850 will likely use all the horsepower your cpu has and will probably not be used to its full potential, thus creating a cpu bottleneck. The 2600xt isn't as powerful as the 3850 so will likely use more of its potential.
It is true that the value of pci-e cards is much greater than agp cards. Check prices at newegg - Sapphire 3850 $105 ($120 before MIR) vs ASUS 4850 $105 ($135 before MIR). I don't know if the 4850 doubles the performance of 3850, but it will definitely mop the floor with it. Likewise, the 3850 performs about equal (according to charts here at THG) to the 9600gso/8800gs and 4670. Both of which can be had for as little as $50 after mir (both cards made by Gigabyte). Thats the same performance for half the price!
Before deciding what card to get, or to completely overhaul your system, let us know what games you play and at what res. I suspect your money will be best spent in a complete new system.
Thanks for all the helpful replies guys. Definitely one of the best forums I've been on. The only game I play on this rig is, you probably guessed it, World of Warcrack. I play it at 1440x900 res which is the max my monitor supports. I use all the lowest settings in game minus spell effects which I really need to have turned up a bit so I don't get myself killed in raids. I have 2 kingston sticks of ram installed at 1gig each with windows xp for my operating system. It used to run fine but all the WotLk effects have just killed my raid and bg performance forcing me to look into upgrades. I really don't need anything too flashy and would hate to have to get a whole new system when everything pre wrath was running just fine. If I could just get 20 ish fps in raids and wintergrasp I would be a happy camper. Thx again for the responses.