MikeZ,
If you are unable to get it working using your current video card and need to perform a cheap upgrade, I'd second the choice of a 6600GT. Best bang for the buck in that price bracket. An ATI 9800Pro is a very close runner-up and is still a fantastic card even now. My old one still chugs along quite happily in my old P4 2.6 LAN rig.
If you really wanted to make the most of that widescreen HDTV, $300 will buy you an X800XT All-In-Wonder. I bought one of these to replace my old 9800Pro in my current P4 3.4 rig, and the number of features and options is simply staggering. It gives you TV and FM tuners, a multifunction RF remote, innumerable A/V in and out options, time-shifted recording of live video and audio (basically a TIVO unit integrated on-card), and is very flexible in display setup. Paired with your 52" TV, it would be really sweeeet.
Good Luck!