Rapid Rick :
Thanks for the initial replies. I'll let you know how it goes. Would it be safe to assume that if I build a whole new system and retain the "old" hard drive, my retail copy of Win 7 will not work? Even in a clean install?
A whole new system will almost certainly require a clean OS install.
The licensing/activation depends on what type of license it is...OEM or Retail.
If an actual Retail license, should be no problem for activating that license again with new hardware.
If an OEM license (likely), then it depends on if the day of the week has an E in it, the particular phase of the Moon, and the type of day the MS rep you talk to on the phone is having.