It was Win7/64 Ultimate, I'd forgotten about the format thing.
Next thing, only a minor niggle. After re-running the Experience Index, the sub-score for my primary hard disk plummeted from (somewhere between 7.5 and 7.9) to 5.9. I can only guess that this is because my PC has decided that my storage HDD has become the primary disk, as I can't see any SSD having such a low score (FYI, my boot drive is a 48GB RevoDrive, and should be the primary drive.) Do you know how I can set the RevoDrive back to being the primary drive?