Matthijs' blog blog post describes the VMC2HV tool you can use to only import your Virtual Server and Virtual PC VM configurations.  You can adjust almost any setting before creating the VM in Hyper-V.

If you are an enterprise user, and want to import many VMs, and manage them after, you will want SCVMM

Migrating to Hyper-V from Virtual Server or Virtual PC - Tips and Suggestions

Sean's blog walks you throught the important prep steps for migrating your VMs from VS or VPC to Hyper-V.
http://blogs.technet.com/askcore/archive/2008/09/19/migrating-to-hyper-v-from-virtual-server-or-virtual-pc-tips-and-suggestions.aspx