Realplayer has alway been kind of a hit or miss thing (usually a miss) mostly because of variations within their own formats which is too bad because I like the idea of Realplayer supporting Linux.
If I were you I would use mplayer over Realplayer since it supports Realplayer as well as many other formats including WMP and Quicktime. Just get the following RPMs from the mplayer web site http://www.mplayerhq.hu/homepage/design7/dload.html
Then grab a copy of mplayerplug-in 2.66 or greater to allow Mozilla to use mplayer. You might be able to find an RPM some where or I can give you a spec file to make your own. http://mplayerplug-in.sourceforge.net/