TV & computer monitor all in one

Is it possible to have a TV be a computer monitor and vice versa.
I'm building a new office in my home and in the office I'd like to have only a single flat screen device in the room.
Bring cable in through the computer?
Or are dual purpose LCD/Plasma units available?
I have been seing a friend's HT with projection TV that also hooked up as a monitor to the laptop extreamly clear and successfull. Since he's only home late evening he's got no problems with sunlight but if you do you would probably want to paint your walls in dark-blue or dark- something.
It's a great option to HDTV if you can arrange a room.
Also on my job very often the new software is demoed through the same setup with projection TV with the great resolution.
Hauppauge has several tv tuner cards to pick from. I have the WinTV Go in my machine and it works really well. The one I have is the mono version. They make them in stereo and with am/fm tuners. They also have released an HDTV card but it's pricey. My daughter has a nicer one in her computer and it's great for video capture and editing also. I think I paid about $50 for the card on sale at Compusa.
There are several options available: Princeton makes larger sized monitors that double as tvs; Pentronics also makes a similar monitor -- I own a 27inch monitor of Pentronics that has a TV tuner built-in and when paired with a computer with a HDTV card could do that as well. Otherwise, I recommend buying a 21 inch or larger monitor and use a ATI All in Wonder card that will do everything but HDTV. The reverse is not true; do not use a regular TV, even a HDTV ready rear projector set and hook a computer through it; computer images will suck and you will burn the screen.
NTSC does look better on a computer monitor because of the monitor's intrinsic higher horizontal and vertical resolutions; although the images are not true high definition, they are sharper.
You can purchase a Video Card that will allow you to recieve coax cable inputs. Relativly inexpensive.