When we released Windows Server 2008 R2 we added the ability to make a virtual machines processor more compatible for migration between different hardware platforms (details here).  Here is a PowerShell script to do this for you:

--> See on Ben's blog ...

Cheers,
Ben

Attachment: ProcessorCompatibility.zip

http://blogs.msdn.com/b/virtual_pc_guy/archive/2011/01/20/enabling-processor-compatibility-with-a-script-hyper-v.aspx