Thank you for the suggestions Devilstar! I found both items on newegg for very decent prices:
AMD Athlon 64 X2 3800+ Dual Core
Gigabyte Socket 939 Motherboard
The only concern I have about the above setup is that the FSB on the motherboard is listed as "800MHz Hyper Transport (1600MT/s)" while the AMD chip has... 2000? Does this kind of "mismatch" lower performance? Otherwise an AGP slot, DDR support, NVIDIA Chipset and USB 2.0 make that one sweet board!
However, since I now have some wiggle room, I decided to explore further (sticking to the general "idea" of the items above, but adding on more power). I have narrowed my CPU choices to the following three (the lowest priced is the one suggested by Devilstar) and am wondering at what kind of performance increases I am looking at if I pay $60 or $160 more:
AMD 64 X2 Dual Cores
I'm at a bigger loss with motherboards because I know so little about them. My biggest concern is the mobo's compatability with the AMD chip I choose and how it will behave with my AGP GeForce card. The following is a list of 10 (ASRock ecluded >_< ) that I simply can't choose from:
Socket 939 with AGP Slot AMD Mobos
To make matters worse, I've come across this
list of "custom" motherboards with exotic names and somewhat confusing (to me) descriptions.
I would really appreciate people's thoughts on this. Once again, I am looking to spend roughly $600 for a CPU/Motherboard combo, although if I can get away with less while keeping solid performance, you won't hear me complain.
P.S. As I mentioned before, this is my first AMD system after a long line of die-hard Intel ones so I'm really excited! Looking forward to reading your replies!