The realplayer binary should be in /usr/local/bin and it will be called realplay. I've also got /home/aaron/RealPlayer8 which contains some dirs called Plugins and Help. I guess your first step would be located those. If it's not in your home dir, try
`$ find / -name RealPlayer8 2>/dev/null`
I'm not sure how exactly you'd go about installing the plugin, maybe I'll give it a try and let you know if it works, and how I did it.