I have a feeling you're talking to nVidia guys! OK, the Rage Theater 200 handles input, yep!
You can access the input using several programs:
1.) ATI MultiMedia Center (ATI MMC) will give you an "Input" program. It's the same as the TV program, but without tuner support since your card has no tuner. You can download this from ATI.
2.) Windows Movie Maker: This is included with Windows XP under Start>All Programs. Is not really set up for watching video "live" as it's a recording interface.
3.) Third-Party programs. You might try some freeware, I certainly wouldn't buy anything.