Windows Virtual PC (for Windows 7 on machines with hardware virtualization enabled) and Windows XP Mode have RTMed and are available for free download at http://www.microsoft.com/windows/virtual-pc/download.aspx. There are many new features in Windows Virtual PC beyond those of Virtual PC 2007 but the feature of most interest to me is the fact that unlike Virtual PC 2007 Windows Virtual PC has an API which allows the virtual machines to be automated. The API is very similar but not identical to the Virtual Server API. If you're interested in this subject then stay tuned as I will be posting the slides and more importantly the code for my Automating Testing Using Windows Virtual PC presentation in the next few weeks.
BTW if you are planning on installing Virtual PC 2007 on your Windows 7 box it will not install with Windows Virtual PC present so you will have to uninstall it first.