I assume you mean re-activate.
If you have to, depends on what you did before you reinstalled.
If you have had the foresight, you may not need to re-activate, when
installing on the same box again.
I mean, if you had saved the 'activation' data beforehand.
To save the activation status, go into Safe mode, back up the wpa.dbl file
from the %systemroot%\system32 folder to a disk or other location. Now you
can put it back after re-install, on top of the 'new' wpa.dbl file.
Note: This procedure is not a hack to avoid activating installations in the
first place and will work only for an XP installation on the same hardware
that you've already activated.
