Office 2007 & dual booting XP/Vista

Back in the good old days, I dual booted a DOS-based Windows version (95, 98, ME) with Windows NT4 or 2000. I quit doing this after XP and ME had some kind of problem. Back then, I would install MS Office and other compatible software first in one OS, then the other, to the same location.

XP and Vista also support dual booting with each other, but in different partitions, but what about office, etc.? Do I have to use separate locations or activation for both, or can I install to the same location, and use the same code?

Does it matter (for any reason - not just installing software) what OS I install first?