How do I setup a software raid 1 on 2 newly installed HD's in ubuntu

How do I setup a software raid 1 on 2 newly installed HD's in ubuntu

I setup a HTPC about a month ago, and just expanded my storage by adding two 750GB drives in addition to my OS drive. I am using Ubuntu 9.10 as my OS and need help setting up a raid 1 on the two 750GB drives.