Why do some movies play much smaller from Hard Drive?

I make backups of my movies so I can play them from the hard drive. In one case, It will play fine on my stand alone, but with WinDVD , I only get a much smaller rectangle. In other words, I have a 42" EDTV monitor, but the image has about 6 inches above and below, and the sides have about 5 inches. If I make a DVD+RW of the files backed up, it plays in correct widescreen mode on HTPC with WinDVD and the standalone.


What could cause this? I am connected via DVI through a Radeon AIW 32MB card, and I use an 848x480 screen resolution. Hopefully someone has seen this before.


Edit: The movie I am trying to watch is 2.35:1 aspect if that helps.


Thanks.