Microsoft made a big splash at LinuxWorld on Monday, announcing the availability of Virtual Server 2005 R2 as a free download. This also will apply to the forthcoming SP1 of Virtual Server 2005 R2. In addition, Microsoft announced the availability of virtual machine add-ins for Linux and a technical product support model for Linux guest operating systems running on top of Virtual Server 2005 R2. Windows Server 2003 R2 Enterprise Edition, will allow you to run up to four virtual operating systems on one physical server at no additional cost, by integrating virtualization as part of the Windows Server operating system. Also, in a move few thought possible, Microsoft has teamed with the developers of the open source Xen product against the market leader VMware, by licensing the Virtual Hard Disk file format to open source specialist XenSource, but not granting a similar license to VMware for rather obvious reasons.