How cheap? Most people here will reccomend the Leadtek card that sells at newegg for ~$50. Never had a chance to use it myself, but judging from all the reccomendations, it must work. The only problem that I see with it is that it is, if I remember correctly, a software-only solution. Which means that it's going to peg your CPU @ 100% usage any time you try to capture. And if you try to do anything while it's working, you might start dropping frames. I had another card - an old Hauppauge - for a long time, and this is exactly what would happen on my computer. It would drop frames left and right if I so much as looked at the computer cross-eyed while it was capturing

. Like I said though, this is just my experience, and with a different card. Somebody (or several people) may come in here and say I'm wrong.
What I have now for video capture is a Hauppauge WinTV-PVR 250. This board has an MPEG encoding chip built into the board, which takes most of the load off of the CPU when a capture is taking place. I can sit here and do pretty much whatever I want while it is capturing, and not have to worry about it. I would highly reccomend it, except for one point: The board retails for $150. I'm not sure if you could find it cheaper on line or not; you'd have to look.
Nate