The SharePoint 2010 Virtualization Guidance and Recommendations white paper is available to download on MSDN.

I really recommend you this great white paper, there are a lot of good guidance and practices about the virtualization  and SharePoint 2010.

This white paper is available on this link:

http://www.microsoft.com/downloads/en/details.aspx?FamilyID=7b50c3ec-abb6-4416-a454-c461bff22e78&displaylang=en