Ok, - dumb questions but I know some of you computer junkies out there can help me!!

Is it only possible to download movies with Limewire pro? If not, then here is my problem - I downloaded a movie, file type mpg, and I tried to play it. When it tried to open in Win DVD, I could hear the sound, but there was no picture. WinDVD just kept playing those crazy light thingys. Is there a specific setting in WinDVD I need to use, or is it just a bad file?

How do I know which files are good or bad? Is there a way to tell?