That would not require you reactivate Windows. Simply use cloning software to mirror your current OS installation to the new drive. If for some reason you want to dump everything on the old drive and completely start over with a fresh install, if this is a full retail version of Windows, there is no limit to the number of times you can activate it. You may have to call Mircosoft and get a new activation number after a few times, and an explanation that is suitable to Microsoft that you are not installing on more than 1 system at a time. That is, if this is a retail version. If it is an OEM version, you are going to have problems if you try to do a new installation.