I just downloaded and installed the Netscape version and it worked fine. It has worked for the last few versions without a problem. Just type "o support" in your address bar and do a search for real audio. Installation is explained there. Direct link: »www.opera.com/support/supsearch/···ndex=365
If it is already installed and you think that you did everything correctly, be sure to select File-Preferences-Multimedia and press the "Find Plug-ins" button. It might help.