If you are just starting to setup your box, its recommended that you download a fresh Mythbuntu image and start from scratch. However, one of the best features of Mythbuntu is that all development happens directly in the Ubuntu archives. This means that you can add all Mythbuntu roles to an existing Ubuntu box.  

Installing

Click this link to install Mythbuntu:

Configuring

Choose System, Administration, Mythbuntu Control Centre to open up the Control Centre. From here you can modify all options that are already setup during a normal Mythbuntu Installation. If you need to setup a backend, this is where you will activate that.