Yep. movies that are 16 x 9 Enhanced (otherwise known simply as "Anamorphic"

contain more lines of resolution to fill the screens of 16 x 9 TVs. However, as long as your DVD player is set to 4:3 mode, the extra lines are removed and black bars are filled in to ensure that the picture looks right.
16 x 9 enhancement is definitely a worthwhile feature (almost all DVDs released these days, esp new releases) are anamorphic. This will become more useful as 4:3 sets slowly get replaced with 16 x 9 sets. TV is going widescreen, and buying anamorphic now simply means that you'll be able to take advantage of the increased resolution (33%!!!!!) when you get a 16 x 9 set.
Actually, if you buy a Sony Wega (other manufacturers offer it too), you can get all of the lines of resolution and still get a correctly formatted picture, even though the set is 4:3. This trick is called "anamorphic squeeze", although that's not the official term (sony calls is 16 x 9 enhancement). Basically, you set your DVD player for 16 x 9 mode (so on anamorphic DVDs it won't remove any lines of resolution). On a normal TV (and even on the Wega before you set it to do the sqeeze), these extra lines will cause the picture to look horizontally squished (or vertically stretched-out... however you want to state it). However, once you set the menu option for 16 x 9 enhancement, the TV squeezes the lines down and fills in black bars. What you end up with is a picture that has 33% more resolution than normal and is also formatted correctly. As an owner of a Wega, I can assure you that it does make a difference and is worth it.
Look for anamorphic squeeze to become a more common feature, as DVD has become extremely popular and it's not difficult to implement.
l2c