VMware has been peddling this vision of companies setting up internal clouds that bridge to external clouds using its promised Virtual Datacenter Operating System (VDC-OS), VDC-OS extensions and a management layer that lets service providers deliver those external clouds that federate with those internal clouds.

That way any legacy, server- or desktop-based application – including those built on newfangled application frameworks – is supposed to be deliverable as a service.

VMware’s problem is it’s selling futures.

Sometime this year it means to ship the first instantiation of VDC-OS and that apparently means the widgetry that pools all the internal compute capacity and delivers it as a service. Until then, it’s limited to progress bulletins and Tuesday VMware Europe opened in France so it had to say something.

Meanwhile it’s dodging bullets from Microsoft and Citrix, which took a pot shot at VMware Monday and freed its XenServer 5 virtual infrastructure – that’s free as in costs nothing – claiming VMware sells the equivalent technology for $50,000 for a 10-server environment, a strike at VMware’s revenue base.

What VMware had to say isn’t quite as sexy.

Only that it’s got its vCloud API, the widgetry that will access internal and external cloud resources, make them interoperate, and turn applications into software-as-a-service, in private beta. Companies like Engine Yard and IT Structures are supposed to be in Cannes demonstrating services built on the thing.

The API gives VMware a chance to sniff about how Amazon, Google and Microsoft clouds use lock-in proprietary APIs – unlike VMware’s which won’t require any application redesign – and how its commodity rivals will never be the serious data center clouds VMware has it mind.

In the name of “open” interoperability between clouds VMware intends to become a standards maven and submit a draft of its API to the Distributed Management Task Force (DMTF). VMware was one of the original authors of its Open Virtualization Format (OVF) standard that its vCloud API builds on.

VMware also says that its vCloud service provider program has grown threefold since September to some 400-strong and includes folks like Terremark, Savvis, Logica, Telefonica, Telstra and Sungard, some of which are currently delivering infrastructure, test/dev and disaster recovery as a service.

VMware is supposed to demo the integration of its Infrastructure Client with external cloud resources at vCloud service providers, the stuff of deploying and managing workloads with these service providers in a few mouse clicks and in the same management interface customers would use to manage their internal clouds.

The idea is that the apps now running in VMware environments will simply be able to run in internal and external clouds.

Meanwhile VMware and Intel, one of its investors – though Intel sold half its position to Cisco late last year – are working to develop VMware’s Client Virtualization Platform (CVP) on Intel’s vPro and Centrino vPro widgetry and will push OEMs to adopt the technology.

VMware’s purpose-built bare metal client hypervisor is supposed to extend the value of desktop virtualization to the client and clients are supposed to be able to manage both VDI and client users from the same image and platform.