Windows XP Product Activation

Product Activation, or Microsoft Product Activation (MPA) as it has become known, was not exactly a welcome addition in Windows XP. It was, however, not introduced in Windows XP, as it existed in late versions of Office 2000, all versions of Office XP, and Visio 2002. MPA works to stop casual copying of software by tying the hardware profile of a computer to software installation.
When dealing with Product Activation, there are three scenarios that can occur. Without exception, you should fall into one of these three scenarios:

• Retail box purchases
• OEM installations
• Volume licensing

These articles, one from Que and one from Microsoft discuss these issues

http://www.quepublishing.com/articles/article.asp?p=102260&seqNum=5&rl=1

http://www.microsoft.com/technet/prodtechnol/winxppro/deploy/wpadepl.mspx