I can only tell you how I did it, not sure if its the recommended
way or not but it worked.
I had already installed it badly so I had the use of the Partition Editor.
I chose the drive I wanted ubuntu to be installed to. Reformat that
drive, create two partitions
one as the / drive and one as /home. Then make sure you install
into the / portion and not another drive as I had done initially
LOL. but no matter if you do, you get to do it over again. Practice
makes perfect :) Might be wise to unhook all other HD's before
you begin installing, that will eliminate the chance of making a
mistake.