I recently downloaded Real Player 10 and installed it on my Fedora Core 2 system. The
real.com website claims that this automatically installs the Plug-in for Mozilla. I verified that
nphelix.so and nphelix.xpt are in my .mozilla/plugins directory. Also Help->About Plug-ins shows "Helix DNA Plugin: RealPlayer G2 Plug-In Compatible". However, if I go to a website such as zdnet.com and try to play any of the video clips I get an error message that says "This contains information of type (audio/x-pn-real-audio-plugin) that can only be viewed with the appropriate Plug-in". I have a similar problem if I try to view a trailer on Yahoo movies. I am not sure why the installed plug-in is not working. Real Player itself works fine, just the plug-in doesn't seem to be working.

just make a symlink as follows,

ln -s /usr/local/RealPlayer/mozilla* /usr/lib/mozilla-1.7.x/plugins/.

It works absolutely fine for me on Fedora Core 2 and Slackware.

Thanks.
Here's another alternative. Just install the rpm (provided at the real.com website). I deleted my RealPlayer directory, switched to root and installed the rpm. Everything just worked for me with no hitch. It automatically installed the Mozilla plugin and I was able to play the embedded video clips at zdnet.com. Mozilla does seem to have a problem playing the movie trailers on Yahoo - I have had this problem on both Windows and Linux. Not sure why.