Hmmm, Aastii is right AGP is an OLD expanson port and since you have an old expansion port that I never even heard of then that means get a new motherboard LOL...Also it depends what you want your computer to do, whether it be a server computer like what this website is on (computerforums.org) or play video games like CODMW2 and the such or maybe your going to use your computer as a workstation...but lets get back on track hehehe....No like Aastii already stated processors fit into a socket on the motherboard.
1. You need to find out your motherboard's socket for the cpu, whether it fits an AMD or Intel and the socket numeral...number...whatever you get the point lol
2. If your motherboard is even is compatible with current CPUs I suggest going to Newegg.com
for buying processors and other computer hardware and matching the socket on your motherboard with socket on the other CPUs.
3. Get the processor for you needs, don't get a dual core processor running at 1.7 GHz and try playing Crysis: Wardhead.
Ok I just researched on AGP and yeah just because you got AGP doesn't mean you need a new motherboard just you can't take advantage of most video cards out there that use PCI Express.