[Snuffy]

Actually you can have all 3 drives with Vista and the same KEY for like versions. You simply can not log on with 2 same Keys at a time.

Swapping keys is very easy... really.. I was for a bit dual booting Ultimate and Premium.. used the Ultimate Key when I upgraded Premium to Ultimate. swap worked fine, since I was not booting online with 2 same versions at the same time..
It was a no no when I used desktop premium Key1 and laptop premium Key1.
so tested by swapping Premium Key with Premium Key 2... all went AOK and I could upgrade both systems at the same time... currently desktop is single boot Ultimate.. deleted all the other boots using BCDedit..manually.. and laptop is back to Premium Key 1. Premium will be in older desktop with Key 2.

The real problems was deleting the #2 and #3 boot versions of Vista..
was more fun than simply FORMAT the drive...