I am currently Tri Booting with XP, Vista Ultiamte and Ubuntu 7.10. Ubuntu is good. I am surprised myself by it. But it takes a lot of work and time to get used to it compared to Windows. If you wish to give it a shot by all means.
Wither that or you can use that 2nd drive as storage for downloads, documents, pretty much everything that you ever want to save in case of a reformat.