VMware's announcement today that it has received Microsoft's seal of approval, under the latter's Server Virtualization Validation Program (SVVP) came as no surprise.

While VMware remains in fear of Microsoft's entry into the virtualization market and its new CEO Paul Maritz, a Microsoft alumnus noted for his pugnacity, has publicly vowed to fight Microsoft tooth and nail, the two simply had to enter a marriage of convenience.

Microsoft would gain a foot-hold among VMware's customers, and VMware needed Microsoft's blessings because, otherwise, it would not be able to run its hypervisors on the Windows Server family. Since Windows Server is a billion-dollar business for Microsoft, that would be a huge loss.

The pain would be most keenly felt in the SMB market, where VMware has tens of thousands of customers, by its own account, and which is a Microsoft stronghold.

There's no doubt, however, that the alliance between the two is an uneasy one. On September 8, one week to the day before VMware's major conference, VMworld, kicks off, Microsoft will make some announcements about virtualization. The technical term for this is stealing someone's thunder.

Whether or not VMware executives hope Microsoft will then be struck by lightning during the launch is not something they will discuss openly; but chances are that sales of Pepto-Bismol will surge in their vicinity.