Well, with your system as it stands now a really fast video card would be a waste.
I would say get an ATi Rage Fury PRO 32MB with video-in/video-out, I got one this past weekend for US$90. It's supposed to be as fast as a TNT2 for 3-D games, not sure how it compares to V3 2k you already have.
Some people say the Matrox G400 but I think the ATi cards with the Rage Theater TV decoder chip is better. Cards with the Rage Theater chip include: Rage Fury Pro 32MB, All-in-Wonder 128 32MB, All-in-Wonder Pro 32MB, and Radeon cards with ViVo.