Microsoft Hyper-V Server 2008 R2 hypervisor (not Hyper-V role on windows server 2008 ) is free to use. There are some 
VHDs for Windows Server 2008 for evaluation/trial. Do these VHDs work with the Hyper-V Server 2008 as well as Hyper-V role? I thought even Virtual PC can run VHDs?
Has anyone been using Hyper-V Server 2008 to lab and practice? I am currently using XP on desktop and win 7 on laptop. I am thinking of installing Hyper-V Server 2008 and several guests for learning towards server exams. I currently use the desktop (Core 2 Quad Extreme QX9550, SAS HDDs RAID-1, 4GB) as my main machine for reading, browsing, and everything. So far, I have only been using VMWare on my laptop to run several instances of Windows Server 2008 R2 guests. It is slow because it is core 2 duo. I have two old servers which do not have VT-X capable processors. Therefore can only run Windows Server 2008 x86 guests only.
Would I be better off sticking to VMWare because I can use a client OS(XP/win 7) and only run virtualization software when needed?
I could also use an additional hard drive on desktop to dual boot to Hyper-V Server 2008. I probably have to upgrade the RAM on both machines. What do you suggest?