That doesn't answer the question: how to DE-activate.
The answer is you don't need to.
You need to *uninstall* from the old computer, and install on the new
computer, and then re-activate it on the new computer. It might say
"already activated" or something; ring the Microsoft number and just tell
them you've switched pc's and no longer use FP on the old machine.
I think FP2000 and possibly 2002 required activation it sent back a
confirmation code that you use if you had to uninstall and reinstall - you
could use the same confirmation code, rather than the full activation
process.
FP2003 doesn't see to do this, it must have some other way of knowing
whether the package is active, or it may treat it as a new (first-time)
installation if you instal on the new machine, even though it is used on the
old machine.
I'm sure this question has been asked before (the exact same wording in
fact).