Laptops usually cme with a 'Recovery Disk Set' which will reimage a hard
drive to 'factory fresh state'.
It may require that you have an identical drive or one very similar in order
for the recovery disk to work: check with the manufacturer for any potential
problems when using larger capacity or drive from other than original
supplier.
Once reinstalled it may not require activation. If it does: you should not
have any problrms with reactivation.
If you have XP as full retail version then you should have no issues at all.
In either case: even if there are errors reported during the activation
process, you can call Microsoft and speak with a representative and they'll
fix you up.