Connecting a TV (even an HD one) to your computer and expecting to use it as a monitor is asking for trouble (once you get over about 20" that is).
A 20" LCD monitor has more pixels than a 720p HDTV and almost as many as a 1080p TV. Now, for a little math:
A 20" widescreen LCD is roughly 180 sq inches, and has 1.7m pixels. That's 9,800 pixels per inch.
A 30" HDTV (720p) is about 384 sq inches, and has just over 1m pixels. That's just 2,732 pixels/in.
Even at 1080p a 30" TV only has 5,400 px/inch (which is probably bearable, but only just).
That's why text, fine line drawings/design, etc look great on a 20 or 24" LCD monitor, but crap on a TV, even an HD one.
My advice: get a nice 27-32" HDTV (720p is fine for those sizes at normal TV viewing distances), and a nice 20" LCD, or a 23/24" if you really want to spend the big bucks. Or you can just do whatever you want.
