My current approach is to have the two Windows 7 OS on two different HDDs (or SSD depending on speed requirements of 64 bit configuration) and connect/disconnect as required. The issue I'm concerned about is whether I can leave my two 1-TB RAID 1 drives hooked up. It's obvious I'll need to install the appropriate RAID management (IRST) onto the 64 bit OS drive, but there are some ominous aspects associated with screwing around with the individual drives in a RAID volume and I want to make sure I don't loose files from the volume.
It looks like I might be able to have both boot drives hooked up and pick which one boots the machine during the MB POST. This is allowed by MS, with the stipulation thy aren't function simultaneously. Being able to keep the RAID Volume connected would make this approach great!