If it is retail then you can migrate it to any machine of your choice. OEM dies with the machine.
With Upgrade version, you need to have a qualifying retail XP or Vista on hand which you don't use again, but it doesn't have to be installed.
When you boot an Upgrade version DVD to clean install to a new HD, you need to wait until after install to insert the Product Key and activate so you can do a workaround given here:
Clean Install with a Upgrade Windows 7 Version The Registry change is much easier I have found.