The 'Leadtek WinFast VC100 XP Video Capture Device' looks good for the money with MPEG I and II hardware encoding (MPEG4 software encoding only). Inputs include Composite/Svideo as well as the usual RF (aerial).
Other graphics cards (more suitable for gaming) have the same composite/svhs inputs also but not all. They're usually marked VIVO I believe but check this as I'm not up on the lingo.
8xAGP graphics cards will be backwards compatible with 4X motherboards (they'll just run at x4 speeds).