Hi Nicksteel!
You should definitely test a soft called Showshifter. It does time shifting, tv capture, dvd player, cd player with cddb, etc. The GUI is designed to be used on TV screen (big buttons) they've done quite a nice job on it.
A very nice think about it, is that it installed and run perfectly at my first try with an ATI AIW 7500. This gfx board is good, but ATI's software package is just a piece of s.. Understand you already knwo about this
You may also want to consider using W2K SP3 instead of XP. It is Microsoft's most debugged OS available right now (according to many video forums).
With the above mentionned stuff and a P4-2.4, I can encode divx realtime with CPU usage at 60% and no lost frames... with a bunch of TSR+NAT+firewall+2 P2P progs running at the same time!!
And if I capture with MJPEG codec (20% CPU), I can watch a movie at the same time.
http://www.avsforum.com/
the "doom9" of pctv
http://www.showshifter.com
http://ruel.net/pc/tv.tuner.frontend.htm
about a prog called myHTPC and other links.