The Microsoft offering, launched Thursday, will enable IT managers to convert some VMware offerings to a Microsoft-compatible format.

Microsoft notes that it has had conversion virtualization software available. "To help ease the migration from VMware to Virtual Server, Virtual Machine Manager converts VMware VMDK/VMX virtual machines to the Microsoft VHD format," Microsoft said in a statement. "If the guest OS runs Windows, Virtual Machine Manager will perform fixes during the conversion process, to ensure a working converted virtual machine."

It will be difficult for Microsoft -- or any other vendor, for that matter -- to dent VMware's virtualization lead, which market researchers place at more than 70% share of the market. VMware has a lead in enabling the use of Unix and Linux, while Microsoft has traditionally been cool to those operating systems.

The Microsoft offering can be downloaded from the firm's Web site. Microsoft VHD format will accept both physical-to-virtual conversion and virtual-to-virtual conversion of VMware virtual machines, according to media reports.