Windows Vista doesn't have native h264 decoding facilities within media center. In order to get this to work with vista you need the TV Pack 2008 installed.
Windows7 however does have native h264 decoding capabilities within both WMP12 and 7MC
I have installed the Vista tv pack, but it seems not to be as simple as x86.
Cant get it to work. Dont know what to do.
So you say win7 x64 works with mpeg4 live tv out of the box?
Just as easy as following directions on this if you want to the codec to work with windows 7 media center. The guy also has a part to make media center working with .mkv files.