If I were running the cloud computing show at Amazon.com (Nasdaq: AMZN) or VMware (NYSE: VMW), I'd be casting nervous glances in the direction of Redmond today. Microsoft (Nasdaq: MSFT) is stepping into their areas of expertise today, all guns blazing. This has happened before, but could it actually work out for Microsoft this time?

The Windows Azure cloud computing platform is old news by now, always playing second fiddle to the first-mover EC2 solution from Amazon. You might even point to similar services from small-cap Rackspace Hosting (NYSE: RAX) and wonder why Microsoft hasn't absolutely annihilated that pesky little competitor yet.

This week, Mr. Softy is doing its best to stake a larger claim in the cloud computing space. In separate partnerships with Dell (Nasdaq: DELL), Hewlett-Packard, and Fujitsu, Microsoft has announced the Windows Azure platform appliance, a hardware-and-software package that makes it easy to deploy cloud services in any enterprise-class data center.

Among the first adopters of this solution is eBay (Nasdaq: EBAY), using Azure boxes to "optimize its platform and achieve greater strategic agility and datacenter efficiency." In plain English, that means being able to add customer-facing services as needed. Oddly enough, in its press release announcing the cloud computing agreement, Microsoft highlighted that its larger public cloud hosting services have been handling auctions of Apple (Nasdaq: AAPL) iPad tablets. Having Microsoft turn the spotlight on that particular implementation in press releases appeals to my twisted sense of irony.

More important, Microsoft has a valuable ally in eBay here; some e-commerce specialists turn to Amazon for cloud computing services, but this one looked to Microsoft. That's how you build a track record and some street cred. Without that, even mighty Microsoft doesn't have a leg to stand on.

Would I sell VMware and Amazon today based on this announcement? Of course not, but I'd keep a wary eye on Microsoft's Azure moves from now on. The Redmond giant isn't leaving the clouds without a fight.

Fool contributor Anders Bylund holds no position in any of the companies discussed here. Microsoft is a Motley Fool Inside Value pick. Rackspace Hosting and Vmware are Motley Fool Rule Breakers recommendations. Apple, Amazon.com, and eBay are Motley Fool Stock Advisor selections. Motley Fool Options has recommended a bull call spread position on eBay. Motley Fool Options has recommended a diagonal call position on Microsoft. Try any of our Foolish newsletters today, free for 30 days. You can check out Anders' holdings and a concise bio if you like, and The Motley Fool is investors writing for investors.