I am choosing which OS to boot by changing the boot order in my BIOS. To me, this seems clean and simple. I built 32 bit XP on one disk, then removed that disk from my system, installed a different disk, and built 64 bit Windows 7.
When both disks are installed, I change the boot order to select the OS I want, and each OS sees and can use the files on either disk.
Am I asking for trouble here, or is this as clean as I think it is? What I want is one set of user document files which can be used from whichever OS has been booted.