Different drives...

I purchased a new pc with a Vista pre-load, and then upgraded over the net to Ultimate.

I have a 750 GB drive installed other than the 320 GB that came with the new PC and the Vista install. I created a partition on the 750 for the XP install. When I attempted to install XO, it said it would erase my Vista intall, (along with Photoshop CS#, Office 2007, etc.).

Is it possible to dual boot by disconnecting the Vista drive, installing XP on the 750 and reattaching the Vista drive? What drive(s) should I make active? Will this be a solution? I realize I'm basically 'geta-testing Vista and a lot of my drivers, software, etc. don't work with it so I want to run XP until at least Vista SP 1...

Thank you so much for for your help.

Tom Wylde