Configuring Windows 2003 Cluster inside Virtual Server 2005...
in my previous project I was trying to setup a Windows 2003 NLB Cluster environment inside Microsoft Virtual Server 2005 to pilot testing middle size server farm installation of Microsoft SharePoint Portal Server 2003 sp1. but failed on some of networking issues. it seems if using one physical adapter to virtualize 2 virtual network adapters in one pc, there will be problems to let the NLB service run properly.
just saw that RoudyBob had a post about Virtual Server 2005 Clustering Whitepapers, it should be worth to read if you are facing those issues.