From the Windows 7 RC FAQ:
"When you download the RC, you'll be given a product key. (See Installation Instructions.) Be sure to use the product key to activate the RC within 30 days, or you'll start getting persistent reminders to activate. Your product key will work for up to three separate computers, so if you want to install the the RC on another PC, you can re-use the same key."
Remember - "A day without laughter is a day wasted."
May the wind sing to you and the sun rise in your heart...