I have gotten quite a bit of questions from people that are starting to plan migrations to Virtual Server. Most people are looking to take existing testing environments or production systems into virtual machines. Some others are have existing virtual machines that they want to migrate to Virtual Server. Help is on the way with the Virtual Server Migration Toolkit (VSMT) which is currently avaialable in Beta. VSMT uses Automated Deployment Services to create virtual machines images of existing systems. I've used it several times to take images of some dev boxes that I've consolidated....work really well.
VSMT FAQ: http://www.microsoft.com/windowsserversystem/virtualserver/evaluation/vsmtfaq.mspx
Beta Info: http://www.microsoft.com/windowsserversystem/virtualserver/evaluation/vsmtbeta.mspx