h264 should be nearly universal. The .mov would work depending on what you put in it, and you could assure the PC user had quicktime installed. AVI off the Mac is likely to be more problematic than anything.
You didn't SAY it had to play in windows media player. You said it had to play on a PC. It will play in quicktime. It will play in VLC, you SHOULD be able to open it with a modern web browser like Firefox or IE7/8.
I don't know that the Mac is capable of creating a WMV file, which is the native type to Windows media player. So an h.264 is the next best thing.