You should check the EULA for your current copy - it may already allow installation on more than PC/laptop, in which case there shouldn't be an issue. In any event, if you're retiring the old PC/laptop and you do encounter an activation problem, you can still do the activation by phone.

There is no facility for 'deactivating' an Office installation. Anything you buy 2nd-hand may have already used all the permitted activations - and may even have been sold to other users as well. You have no way of knowing until you try to activate it - at which point you may find you still have to use telephone activation and, even if you don't, you still won't know whether you've reached the limit.

__________________
Cheers,
Paul Edstein
[Fmr MS MVP - Word]