You friend sent you a video file (probably taken using his special camcorder) but your computer doesn't seem to have the right codec to play it. Well here's the simplest way to be able to play almost any video file you ever encountered..
1) Remove any other codec packs/special video player that you've installed.
2) Install K-Lite Mega Codec Pack. It uses windows media player classic as the base player which can play almost any video file format when combine with Klite. It can play rmvb, mov(quicktime), mkv, avi, mpg, or even flv(youtube)! Also plays DVD and VCD.