Not quite sure what you want to do. Are you asking if you can install a copy of windows on a computer using the an activation code that you have already used on another computer? If so, then the answer is no, you can't do that. The windows license specifies that a copy of windows can only be installed on one physical computer at a time. If you install Windows on another computer then you have to buy a new activation code to activate windows on that computer. The rule applies to all copies of windows regardless of the version. However, if you are migrating to another computer with a retail copy of windows(not OEM), then you may be able to call Microsoft and get them to activate your copy of windows on your new machine while deactivating the copy on the old machine. Keep in mind that a migration activation is entirely at the discretion of Microsoft.