Windows 7: Move 7 Pro Upgrade to new machine

Licensed Windows 7 Pro is on my home built machine.

The OS on this machine started as Windows XP Professional, full version, not upgrade.
Upgraded to Vista, upgraded to Windows 7 Pro, all on the same machine.
A couple of new HD's, no problems.

I'm finally building a new machine and going to install the 7 Pro Upgrade.
I could move the HD from my old machine want all new.

What do I need to know?

Thanks,
Pete

Since the underlying XP is full version and can migrate freely, it qualifies you to use Windows 7 Pro upgrade version (which can also migrate freely) on the new rig.

Nor does the XP need to be installed to serve as qualifier - you only need to not use it or use it as a qualifier for any other OS while it is serving as qualifier for the new rig.

To install upon a new HD leave the Product Key blank when first asked, then after install do the quick registry workaround given here to activate Upgrade version on a new or cleaned HD. Clean Install with a Upgrade Windows 7 Version

If the HD has another OS on it, the installer will see it to allow Upgrade version key upfront even if you go on to use Custom install>Drive Options to Delete, Create new and Format partitions.

I've compiled a series of steps to get a perfect reinstall based on hundreds done here - use the ones which apply to your situation: Reinstalling Windows 7

After double in-place Upgrades you should really enjoy the difference with Windows 7 in it's native clean-installed state!

Just what I was looking for.
Couldn't remember the step about leaving the Product Key blank.
If I remember, there was a lot of chatter about this right after the last Windows 7 RC.

Many thanks,

Pete