I just went through this whole drill, ready to buy a widescreen HDTV and decided to do nothing for right now because of the potential damage to screens/projector guns from extended sessions of wrong format. The technology is out there but unfortunately the broadcast industry will not be deliverying any substantial HDTV for another 2-3 years. There are very few channels, cable, satellite or off-air that are delievered in true HDTV Widescreen which means the majority of your viewing is still going to be 4:3. DLP sets are the only ones which are not vulnerable to burn-in but they still come at a premium compared to rear projection TV's.
Unless your current TV is dead, I would hold off. Even then, unless you only view DVD video, I would still suggest you pick up a cheap conventional TV to hold you over. There are bargains in the 27" and 32" models, such that after 2-3 years it wouldn't matter if you tossed it off the proverbial pier and bought a widescreen HDTV then, which will be better and cheaper than today. Plasma screens may even be viable then...a 42" set mounted on a wall is so cool and smart. A very interesting exercise to go through before buying a RP widescreen, DLP or Conventional is to get the dimensions of the footprint and map it out in your viewing room. The Mitsubishi 55" RP HDTV, which I was leaning toward is 50"W X 26"D X 50"H. That doesn't sound too big on paper until you start to try to figure out where to place it and rearrange furniture.
It's a real chicken-n-egg situation. Given the timing, it doesn't make any more sense to purchase a HD 4:3 set, more than a 16:9 model.