Microsoft has recently posted the BizTalk Server 2009 Hyper-V Guide. You can find it here.
Here is a short description of Guide:
"The purpose of this guide is to provide practical guidance for using Microsoft BizTalk Server 2009 with Microsoft Windows Server 2008 Hyper-V. The emphasis is on BizTalk Server, but the performance evaluation methods and performance testing scenarios are useful for analyzing the performance of virtualized server applications in general. This guidance will be of interest to both the IT Pro and Developer communities."