I'm new to all this and I've been downloading movies in avi and mpg. My avi's seem to work great on Windows Media Player, after I downloaded (and even paid for some) half a dozen players that didn't do the job. Now I've got all this junk on my computer I don't really need.
Wish I had more technical answers for you, but I've got only experience. I'm not good at deciphering the help files, so it's trial and error for me.
I hope the Windows player will work for you. If you've already tried it, try it again and play with the settings. That's usually how I get something to finally work, though I end up never remembering what I did, so I can do it again.
Lots of luck!