Now this MARS scape I downloaded last night works great, just don't know why.
If you can run the Mars dream then it looks like your able to run dreams that are created from WMV videos. Muckyman mostly uses WMV and Mars was created by him. If you want to confirm this try downloading other dreams created by him as he has made alot of nice ones. His gallery can be found here.
I have created a couple with WMV but I mostly use MPEG2 as they use a lot less CPU to run.
Can't find a freeware decoder, do you know of any good ones?
You can get a free MPEG2 codec by downloading and installing Virtual Dub. I would uninstall all of the codec packs that you have installed trying to fix this before installing. Once installed you should be able to run MPEG2 dreams.
If you still can't, you may have a codec installed that's conflicting with one of your other codecs. In this case you can install Installed Codec to help you figure out which one is causing the conflict. I would use it to disable your codecs one at a time until you find the culprit.
Good luck.