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.

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iMac G4 OSX 10.3.9
RAM 256MB
LW 4.10.5 Basic
ADSL anything from 3 to 8Mbps/around 1024kbps

"Raise your can of Beer on high
And seal your fate forever
Our best years have passed us by
The Golden Age Of Leather"
-Blue Öyster Cult-