RAID in Ubuntu can be setup during the install using LVM. I had a box that was running RAID-0 for a while. (I was very fortunate it never failed on me!)
It can take a time or two to get the RAID correct if you haven't done it before. Just be patient and use Google.
There's an article floating out there on how to set up an $80 fileserver in 45 minutes that is an excellent resource if you want to use Ubuntu. Just ignore anything you don't want to use.
The Ubuntu route is very secure and very manageable. And, there are a lot of people out there who can help you with issues. Not to mention its free!