Just as everyone said, the resolution on an LCD TV isn't going to be as good as on a monitor... on the other hand, if you go smaller it's going to make less difference.
For example, a 37" LCD isn't going to look very good at 18" away, but a 26" might be acceptable. (22" LCDs are 1680x1050 and look great, to most people. 1366x768 at 26" might be alright if you like big buttons/text anyways which lots of people do for various reasons).
Make sure you get a TV with DVI or HDMI (which you can connect to your computer via a DVI->HDMI adaptor) input though, as anything else is going to look awful at that size/resolution/viewing distance.