In order to solve "Windows Media Player won't play MP4 files even when the appropriate codec is installed" and to successfully play any MP4 video in Windows Media Player, we had better
convert MP4 to Windows Media Player more supported video format like WMV, AVI.
This worked great on both my windows XP and windows vista- both 32bit. I did the recommended easy install. I would recommend that during install it will ask if you want internet tv on your desktop- click decline, it is nothing more than anything already
on the net but this ad on puts an irritating bar on the right side of the screen.