I am afraid not. I was on the same case, and unfortunately for you, any version you have of WindowsXP or Vista64bit would generate a new key, so if you have dual boot, you would need two keys, to avoid the hazzle of having to re-transfer the license everytime you play with the different OS'es.

I am not sure about Window7 yet, when i tried it earlier in BETA it had serious problems with PIP-functionality, although, the OS might have matured somewhat since then.

Buy two keys...its cheap, and goes to a good cause, further development of the program...hehe...