Inside Windows Product Activation
Product ID
The Product ID consists of five groups of decimal digits, as in
AAAAA-BBB-CCCCCCC-DDEEE
If you search your registry for a value named 'ProductID', you will discover the ID that applies to your installation. The 'About' window of Internet Explorer should also yield your Product ID. You can also find the Product ID by right-clicking the icon "My Workplace" and choosing "Properties".