By default PocketPC only has a WMV player (I tried to check... but MS's WindowsMobile site is messed up, and won't actually give me the content), and to my knowledge the only WMV encoder for the Mac is commercial. However, there is a
build of VLC that you might want to try that allows for a lot of other codecs. It looks like that project is still working out a lot of kinks, so it might be hit-or miss.