Converting a Citrix XenServer VM to a Hyper-V VM is supported, and it is done using the P2V process. The procedure described in this recipe is exactly the same as the one used to convert physical servers to Hyper-V VMs.
Note
VMM 2012 R2 no longer has the P2V feature, and now it is not possible to use VMM 2012 R2 to convert a XenServer VM to a Hyper-V VM or perform other P2V conversions.
The steps described in this section are valid for the VMM 2012 SP1 version. An alternative is to use the Disk2VHD tool, for which the P2V process is described at http://social.technet.microsoft.com/wiki/contents/articles/9790.hyper-v-p2v-with-disk2vhd.aspx. You can also use third-party tools such as 5nine Migrator, which offers P2V, V2V Migration, and Capacity Planning, and can be found at http://www.5nine.com/p2v-migration.aspx.
However, note that only running VMs are supported for the conversion in VMM 2012 SP1. The source VM must also be running a supported Windows...