The best of the best in the "TV" market is going to have a 1080i resolution. (Few brands get up to 1280). Basically this is the same top end resolution as your average 17" flat screen monitor. (This is approx 1920x1080 resolution)
So if you get a larger scale HD TV... keep in mind, you will likely be unhappy with the look of the graphics. For instance I have a Sony 42 Grand Vega LCD Projection TV. At 42" it is basically functioning at or around 6X my 19" monitor on my computer. (Like have 3 monitors wide and 2 monitors high) However if I plug my computer into it in HD mode (Wide Screen) I am only running a resolution that is 320 pixels wider, and about 500 pixels LESS tall. You are however sitting several feet away which does help reduce the "grainy" look. However if you are serious... I recommend getting a Nice Monitor (Something in the 4 million pixel range will be 2x the BEST HDTV) and then getting an HD TV card. If you want to go all in one.
However, if you are interested I would recommend you talk to the Computer retailer in your area to see if they know of any such setup you cuold see (Computer and HDTV as monitor)
GE-Raven