When looking up specifications for a rear-projection TV, it is worth treating them as with looking for a projector.
Standard projector systems like those used in presentations project an image on a screen. Rear-projection TVs work the same with the exception that the screen and projector are built in to a fixed single unit, the screen is translucent and the projection equipment is fixed behind set within the set.
Specifications such as DLP/LCD technology, contrast ratio, lumens work the same for both front and rear projection systems. I plan on setting up a thread to give more detail on each each specification is about, although you will find some useful information on Howstuffworks's how projection TV works. This shows a good explanation of each system; both rear and front projection
DLP and LCD each has its advantages and drawbacks. LCD uses similar technology to a TFT monitor by blocking light using individually coloured pixels. DLP uses pixels composed of miniture mirrors which alternative back or fourth to show or hide a pixel. As a result DLP gives higher contrast ratios and darker 'Black' than TFT as you may have noticed. However TFT tends to have supperior colour rendering to DLP.
The main things to look out for are contrast ratio and lumens. Many manufacturers try sticking on bonus features to tempt users to their products so look at the specification first. :eek: Lumens specify the maximum light output (like that of a light bult - 750 lumens = ~60 watt everyday light bulb). Contrast ratio specifies how many times the brightest white is compared with the darkest black. Just note that some models aim to make their contrast ratio look impressive by brightening the bulb on bright secenes and reducing it on night time or dark scenes.
Happy TV hunting