Real Player should be in the repositories but is called Helix player. It is
the open source version from Real Audio. You can also download and install
Real Player from Real Audio and install it from deb.
forms.real.com/.../RealPlayer11GOLD.deb

If you add the Medibuntu repositories then you can install RealPlayer 10
from their repositories using Synaptic.

Here is how to add Medibuntu: https://help.ubuntu.com/community/Medibuntu

Ailurus and Ubuntu Tweak will also install Real Player for you. Ailurus:
http://code.google.com/p/ailurus/ Download the deb from the right side. when
it is downloaded click on it and it will open Gdebi and offer to install it.
Ubuntu Tweak is available from Getdeb.net:
http://www.getdeb.net/software/Ubuntu%20Tweak

These are two good utilities to have anyway to get the most out of Ubuntu.