People keeps asking me what I would recommend for a home theatre PC (HTPC). LCD or Plasma? In general I would recommend a good LCD. I know that the problems with burn in have been close to eliminated on the best plasma screens. Still, I find the crisp and clean LCD picture with absolutely no burn in problem preferable. A quick roundup:
Cathode Ray Tube (CRT)
First of all, it is perfectly OK to use your old tube. A standard cathode ray tube (CRT) connected to a PC through S-Video or even composite video should work fine if you adjust your screen card and use a proper media center software. The whole point of these softwares is to give you a front end from your computer that looks good even on low resolution television screens.
A quick trouble shooting tip: if you get a black and white signal from your PC when connecting through S-Video you probably have to select the correct output (S-Video ro Y/C) in your screen settings. If you get black and white when connecting through composite you probably have to take a look at the video format settings. Choosing NTSC when you have a PAL television could give you a black and white picture.

Liquid Chrystal Display (LCD)
LCD has been used for computer screens for some time. For the last couple of years they have been able to produce them big enough for use as television sets. Only half a year ago it was a problem that the contrast ratio (the difference between black and white) was too low. Resulting in loss of detail in dark and bright scenes. Now, that is about to end. Some of the vendors has introduced LCDs with contrast ratios of 3000:1 and 5000:1. Earlier that was only possible for Plasma displays. Another problem was response time. Bad response times could result in problems with fast moving video. Now, most LCD screens have a response time of 8 milliseconds or better. That should be enough for most people watching video or playing games on their screen.

Plasma
Plasma screens traditionally gives better contrast ratio, a more correct black level and in general a slightly more soft picture. Half a year ago a good plasma would without doubt outperform a good LCD in quality for watching movies. Right now that have changed because of better LCD panels. In general you have to pay more for a proper high resolution plasma compared to a high resolution LCD (a resolution of 1280 x 720 or more).
And for the people that want more than a quick round up:
Wikipedia: CRT, LCD, Plasma
Comparison: Plasma vs. LCD TVs
And yes, the pictures in this post are all super close ups of the described technologies. With compliments to my new Canon S2 IS!