Three or four things-
1) Get a HARDWARE one. Don't expect USB to handle the intense bandwidth that TV will pass through. Anything on USB will use software for its data transfer, as opposed to hardware, where it's controlled by dedicated hardware. You'll find it's a little more dedicated.
2) If you're outlaying the dollars, don't do it for analogue tv. Get digital and HDTV. You'll love it.
3) I can recommend very highly a TwinHan card. They do satellite, terrestial, cable etc etc.
4) If you can, use
http://nate.dynalias.net/DigitalWatch/ it's SUPER software for your card. Super. Does BDA etc, too.