Dual boot: Vista and Vista on 2 Hard Drives?

There are many articles on how to dual boot Vista and XP, but I want to dual
boot Vista and Vista, with an existing installation, on 2 Hard Drives.

Currently I switch these in the BIOS, but I'd much rather chose at a later
stage, can this be done?

Why? Because I keep one of the drives for random software that I rarely use.