If you have the V3 3500TV, the TV tuner program should have an option for video capture. Just keep in mind, anything with decent compression (DivX, MPEG2) will eat even the best processor for breakfast at anything resembling a high resolution (my TBird 900 croaks at anything more than 400x300 DivX, and this is writing the data to an IBM Deskstar 75GXP). By this I mean you'll start dropping frames left, right and center.
If you have a huge, insanely fast HD, you could do some very basic compression (forget what codec is good for that, but do NOT do full frame uncompressed) and reencode when you have the video on your hard drive, not having to worry about it being done in real time (so you can do it in higher quality).
Personally, I'm picking up an ATI All-In-Wonder Radeon for this sort of thing, and supposedly it does MPEG1 and MPEG2 in hardware. Very nice.