some DVDs i have say "2.35:1 enhanched for 16:9 televisions". What does that mean?
it means the encoding on the dvd is to preserve the full resolution of the image. basically, (and wooch or sirttt or anyone jump in and correct me if i'm wrong) but the way they encode the discs is that if it's preserved in its original aspect ratio (widescreen) then when it plays back on a 4:3 tv, it is "playing" the bars on the top and bottom of the screen.
that is, the entire image encoded on the disc is in the shape of a 4:3 screen. its just that the part of the image being displayed are the black bars (to preserve the full image of what was captured by the camera). the dvd is sending a 4:3 image to the tv.
if it's 'enhanced' then the encoding is to fill the screen basically. the entire image encoded on the disc, is in full resolution in the shape of a 16:9 screen, there are no black bars encoded on the image on the dvd. here, the dvd is sending a 16:9 image to the tv. kind of like the anamorphic filming process where the lens squeezes a wider picture onto the film. if you were to see the enhanced picture on a 4:3 screen, it would look mushed, elongated-wise. but when played back at wide, it fills the frame. this process incressed about 25% resolution from watching a normally encoded widescreen disc on a 16:9 tv.
2.35 simply refers to the aspect ratio that the director chose for a particular film, and the framing that's used on the DVD. "Enhanced for 16:9" means that the picture was anamorphically formatted so that the image contains greater vertical resolution. On a 4:3 TV, this extra resolution is not used and will play back as a regular letterboxed image (unless you direct the DVD player to play at 16:9 in the setup menu, in which case the image will not have the big black bars on the top and bottom but will look squeezed instead), while on a 16:9 TV the extra resolution will stretch out over the full width of the TV with much improved picture quality. Here's a site that shows what anamorphic enhancement does.