With Windows 7 it is easier than ever to multi-boot - I highly
suggest, though, that you get another physical HD to instal *nix on and go that route. Another alternative would be to use a VM software, like VirtualBox or VMWare Server.
if you're familiar with both, and want access to both simultaneously, VM would be the way to go. if you don't care about being able ot access both simultaneously then dual booting would be the way to go.
These days you can do just about everything in *nix that you can in Windows (with the exception of playing certain games). Since you're already comfortable with both OSs, I'll spare you the side by side comparisons.
Oh, just saw - new beta out for VirtualBox.... VirtualBox Free Download and Reviews - Fileforum