Microsoft is getting aggressive in the hypervisor wars and, to this end, has released a beta version of their Virtual Machine Converter Solution Accelerator. This tool converts both the VMX and VMDK files to Hyper-V formats.
The current version of this tool is still in beta and can convers VMware virtual machines created with VMware vSphere 4.1 and 5.0 to Windows Server 2008 R2 SP1 Hyper-V and Microsoft Hyper-V Server 2008 R2 SP1.
Microsoft demonstrated this tool at TechEd 2012.