Many Vista installations included both Media player and the "Appleish" Real Player in the default setup. This was especially true if you got a computer with the OS (and always a few undocumented "free junk" things) pre-installed.

In the past, there have been some media files that would only play in one or the other of the two media programs. A difference might be that your Vista had both programs installed. Real player is NOT installed with any Win7 that I've heard of, so now you won't have it.

You probably can add Real Player (or whatever other thing Macs use now) to your Win7 installation, if you'd like to try it. If you can find it, it should be a matter of "click to install" and then you'll have it, but you will have to go get it and intentionally install it as a separate program for Win7.

With both player programs installed, selection of which to use for a given file was automatic in older Win versions, but might not be as automatic in Win7.

I;ve seen so little "tech advice" in sources that used to be useful that I can't really say what the state of the art is with the newer Media player, but "another player program" might possibly make your problem files playable. If it doesn't, removing Real Player has always been simple and clean in Control Panel|Add/Remove Programs. (I removed it lots of times because it was "rather buggy" in earlier Win versions.)

John