So officially HyperV can only be managed from Vista or Server 2008. But according to http://technet.microsoft.com/hi-in/library/bb740951(en-us,TechNet.10).aspx it says the Virtual Management Console will run on XP Pro SP2.
And VMM console is supported on winXP 32 bit and 64 bit.
The VMM console basically connects to the SCVMM server which can be installed on a Win2003 sp1 or sp2 both 32 bit and 64 bit. And that connects to your Hyper-V.
How about running Vista in a VM on your XP machine and connecting to your HyperV server.
People have also been seen using RDP to connect to the windows 2008 box and manage Hyper V.