Yo boots, there are many people who will tell you that Real is beyond crap (count me among them, of course) so my suggestion for the day: don't use it.
Try a free player like
VLC or mplayer (click the link for VLC or look in google for player). Both need no additional codecs.
If you want to use, say, WMP (windows media player, eh) you haveta dld the nimo pack that contains most (if not all) of da codex for ya.