Hmm... well, after some rummaging, I think I got something. We'll see how this goes. Word of caution, though: first off, I haven't tested this myself... I dunno if it'll even work, much less if WMM will like it. That, and an AVI container isn't suited for h.264 videos... there are features of the encoding which aren't allowed by the AVI container.
Alright. Well, after looking around a bit, I came across the tool that "should" let you dump that .h264 file into an AVI. Download the tool AVC2AVI from . The tool comes with its own GUI, so you can work with that.
Run the GUI, put in the path for the .h264 stream, and press the Mux button. I can't really envision you needing to change the FOURCC, and since it's AMVs we're talking about, framerate is kinda a moot point.
Hopefully the AVI that comes out the other end will work in WMM or something.... we'll find out.