Both Magnus and Ray are wrong about "anamorphic". DVDs can be anamorphic regardless of what shape the movie itself is.
16:9 films are films that say they are 1:1.85 or 1:1.78. They completely (or very nearly completely) fill up a modern 16:9 set. The logo on the back will look like this or this:
Films that are 4:3 will usually have either the following logo or the words "full screen" (though you'll see less of the words "full screen" now that modern tv screens aren't shaped 4:3 anymore) :
Films that are even wider than 16:9 are usually identified with this one: though as you noted some are 2.40:1.
When they designed the logos, they intentionally made them in the shape of the movie. So you don't need to memorize the numbers, you can just recognize the shapes (square-like is 4:3, rectangular is 16:9, really-long-rectangle is beyond 16:9).
"DVDs can be anamorphic regardless of what shape the movie itself is."
Will, Uhm, a 1.33:1 image cannot be anamorphic, right? And I think you're also being misleading. Just because a DVD case says the movie is 1.85:1 or 2.35:1 doesn't mean the image is anamorphically enhanced.
Jeff, You'll probably want to look for two things: 1) the aspect ratio, such as 2.35:1 or 1.85:1 or 1.33:1. This is basically the width to height ratio of the image. And if you're a purist, you'll probably want to see the image the way it was displayed in theaters. For example, the Harry Potter movies were shot and projected with an image in the 2.35:1 ratio. The DVDs are available in 2.35:1 (widescreen) and 1.33:1 (full frame). The 1.33:1 version is cropped down to fill a 4:3 TV set. On a 16:9 set it will have a squarish image with black bars on the sides. The 2.35:1 version represents the movie as it was seen in theaters. For older movies shot in the 1.33:1 ratio (Citizen Kane), there will probably only be one version available, and it'll have black bars on a 16:9 display unless you s-t-r-e-t-c-h the image (yuck!).
2) look for whether or not the disc has been "enhanced for 16x9 displays" or "anamorphic." Depending on the size of your display, you may see a significant improvement in image quality with enhanced discs.
The good news is that most widescreen movies released now are anamorphically enhanced (excluding the Star Wars original theatrical versions!), but if you're going to be shopping for used discs you'll have to be more careful. Many movies have been released in various versions, and you'll have to have sharp eyes to avoid picking up a favorite movie in the wrong aspect ratio, or unenhanced. Happy hunting!
I think the OP's question (Jeff_A_G, please correct me if I've misinterpreted you) is whether a certain title will display correctly on a 16:9 TV.
To use one infamous example, each of the latest "Star Wars" original trilogy sets contain two discs. Disc 1 is the "special edition" of the movie, and is presented in "widescreen format enhanced for 16:9 TVs" and will display correctly on a 16:9 TV. Because the film's ratio is 2.35:1, you'll get narrow black bars at top and bottom, but the image will fill your screen's width. Disc 2 is the original film, and is presented in "4:3 Letterbox format." The ratio of the image is still 2.35:1, but it will NOT display correctly on a 16:9 set -- you'll get black borders on all four sides.
Check out this example at TV Shows on DVD, about the non-anamorphic release of "House" last year:
Looking for the word "anamorphic" or the phrase "enhanced for 16:9 TVs" is probably your best bet for determining whether it'll display correctly on a 16:9 TV. If both of those are absent from the packaging, you might want to do some research online before buying.
***Oops, I was writing while Don was posting! Sorry for being redundant!
I have, at least in part. All of the 1.33:1 shots in the THAT'S ENTERTAINMENT trilogy of films are enhanced for widescreen TVs despite being in the 4:3 ratio. Similarly, "The Sorcerer's Apprentice" in FANTASIA 2000 is also enhanced within the 4:3 frame within a movie where every other segment is 1.78:1.
I suppose the really knowledgeable tech-heads can correct me, but I thought by definition, a DVD frame is 4:3, 480i? And anamorphic 16:9 means squeezing in a 16:9 frame into the 4:3 frame. Consequently, a "regular" 4:3 frame is, in a sense, anamorphic, but meaningless on a 16:9 TV since it is then "incorrectly" stretched, and for best results you should use a "squeeze" function that squeezes the stretched 16:9 image back to 4:3?
As I understand it, anamorphic is a way to use maximize use of the available horizontal lines of resolution (480), instead of wasting space hard-coding the black bars.