If you have installed Maya 2012 on Ubuntu 11.04, you can install Mudbox 2012 only, otherwise you'll need to install all stuff (flexnetclient, flexnetserver...) and check out if you have all required packages.
Maya 2012 x64 is incredibly fast on Ubuntu 11.04. Unfortunately Autodesk doesn't support Ubuntu and the packages we can download are rpms. Anyway, I'm trying Maya now and it works very well on ubuntu 11.04. Here the steps I followed to install Maya 2012 Hotfix 1: