Howdy folks,
I rushed that thread Tuan linked, in a nutshell PUNKbuster could be the problem, I played FC stand alone, and I never installed punkbuster with anything, so I cant verify.
If that is the issue, I hope it's listed in uninstallable programs, or what I found quickly searching was to delete the folder pb (I'd just rename pxb for testing).
I very recently saw FC2 for $20 (maybe even $10 in a small jewel case) in a store locally, so that has come down finally, though I didn't buy, I haven't had a itch for an FPS in a while and I still have Painkiller standing by when I do and PK definitely runs great on pretty old systems if you need substitute.