Well My 2 cents
Dual Boot
Either get another HD or partion it, if it's large enough.
I have three HD's in my system.
One of them is split into 2 partion's Front side 50 gig is my working OS for anything other than Gaming, Back side is Games, IL2,COD4, list goes on. 150 gigs of them.
Second drive front side is 15 gig for my Gaming OS just the basics,(18 processes running on fresh boot) and a few utilities for the games and hardware. Back side of that one is 97 gigs and it is My Documents, which by the way is linked to both OS, so no matter what one I'm booted up to clicking the My Documents icon takes me there.
Now the only change I'm considering is getting an external now that they are getting so cheap is to put My Documents on it, just for a more secure feeling of them being less apt to lost to