Did you try searching? This was posted earlier today...
http://www.tfproject.org/tfp/showthread.php?t=72406 ...
And it's an almost identical question to what you have. Buying a new video card is unnecessary and expensive. I would recommend a video capture card (not a graphics display card), simply because PCI will most likey be faster than USB solutions. Not to mention it's nicer not to have stuff hanging out of the case. But that's just me.