If you read the graphics card section of this forum, I expect you'll find some pointers, though to be honest, you're not going to find anything that'll set your system alight if it only offers a 4x AGP port...
Best bet would be either a 7600gt($185) or a 7800gs($235)
Indeed it will. But as I said... it ain't gonna be setting his system on fire with blazing fast throughput and silky smooth DX10 visuals...