I know this isn't entirely System Center Virtual Machine Manager specific but it's a popular topic and I thought it was relevant enough so here goes:
As I'm sure you're probably already aware, support for Windows 2000 and Windows XP SP2 ended yesterday and I wanted to let everyone know that the Hyper-V support statement for Windows 2000 and Windows XP SP2 virtual machines has been published on TechNet.
Hyper-V support statement:
Support for Windows 2000 Server and Windows XP with Service Pack 2 ends on July 13, 2010. After this date, integration services for these operating systems will not be updated and support will not be available for any issues arising from using these operating systems in virtual machines. For more information about the end of support, see Support for Windows 2000 and Windows XP Service Pack 2 (SP2) Ends on July 13, 2010.
Hope this helps,
J.C. Hornbeck | System Center Knowledge Engineer