There are a couple of recent announcements with regard to the current range of products that I thought I would cover off. One is about licensing and has been written up by Matt McSpirit at http://blogs.technet.com/mattmcspirit/archive/2007/06/22/microsoft-virtualisation-licensing-client-and-server.aspx...
I’m not sure how many people are aware of this, but if you buy a Windows Vista Business or Ultimate then you can use a Windows XP CD (which you have legal access to) to load Windows XP onto that machine. When you need the product key / or need to activate, this will potentially fail, but a quick call...