You have a few ways to do this. If you are doing a few migrations then the tool that Joe pointed out is good. If you're doing more and want to have more control, then you'd set up VMM to connect to your vCenter and do a V2V conversion. If you have 100+ VMs then there's a new package solution based on System Center 2012 that is based on automation, self-service, and governance: http://www.hyper-v.nu/archives/hvredevoort/2012/04/virtual-machine-migration-toolkit/
We currently have 7 VMWare hosts that are running about 30 of so guest servers. We will be moving to HyperV this summer, ours is mostly due to cost and the fact that we never use all the bells and whistles of VMWare. We are a K-12 school division if that sheds any light on the pricing angle :-)
We are running side-by-side and maintaining our current VMWare licenses, but will not be purchasing anything additional.
Michael D'Angelo (former)MVP-MIIS, Pace University Senior Systems Administrator (Windows)(MS)NMDANGE PhoeniX WorX Systems Administrator. If you play Total Annihilation, please join us. http://www.phoenixworx.org