We have 2 physical server with 64gb ram 4 socket of quad 2 core RHEL 5.3 XEN install on top win2k3*8(8 server of win2k3) and win2008*4(4 server win2008) running is any tool at open source to manager all these from winxp or ubuntu 9.04 client. Which can give live migration feature, fail over migration each other.
pls ignore with my write skill.
Sounds like you really wanted to go with Citrix XenServer. It supports most of the features you are asking for out of the box with the free version.
Though in order to do live migration, you would want to set up a separate storage subsystem (some sort of iSCSI, NFS, or NAS solution)