Microsoft will release the source code to part of its Silverlight technology at MIX 07 this week, according to sources familiar with the company's plans.

Sources said Microsoft will also release a beta of Silverlight, a recently unveiled browser plug-in that allows websites to offer video and interactive media interfaces. The technology uses Vista's new graphics framework, Windows Presentation Foundation (WPF), and Microsoft is promoting it as a direct competitor to Adobe's Flash.

Specifics on which aspect of Silverlight will be open-sourced were not available, and Microsoft's public relations firm declined to comment.

The final version of Microsoft's Expression toolset for building rich Internet applications (RIAs) also may make an appearance at MIX 07, according to sources, though Microsoft has two more months to work on the tool according to its schedule. The company has said Expression, another product it hopes will woo RIA designers away from Adobe, will be available before the end of June.

Microsoft is pitting Expression as an alternative to Adobe's recently released Creative Suite 3, and the toolset is also key to Silverlight because the company hopes designers will use it to create applications to be delivered through Silverlight.

Microsoft's rather unconventional move to embrace the open source community could be a response to Adobe's announcement last week that it will open-source the SDK for its Flex RIA development environment by the end of the year.

Adobe has a multi-year head-start on Microsoft, and open-sourcing components of Flex should grow that base, users have said. Microsoft likely sees a need to lure developers to Silverlight as quickly as it can if it wants to catch up to Adobe.

Microsoft hosted its first MIX show last year as an appeal to web designers and developers of RIAs, an audience whose respect the company has yet to win. Microsoft has made several stops and starts in offering web authoring and design tools over the years, but the company has had far more success among developers building desktop applications because of its Windows and Office products.

Keith Cutcliffe, IT developer and analyst for ProAssurance in Alabama, said he has reviewed tools in the Expression suite, and from what he's seen it's a solid product. "However, I stand by my belief that Microsoft just doesn't know how to appeal to the designer crowd," he said. Cutcliffe attended MIX in its inaugural year, but is not attending next week.

Strategically, Microsoft is trying to make the necessary leap to the web as a platform for developing applications to compete not only with companies such as Adobe, but also companies like Google and Yahoo. It's important for the vendor to make inroads with developers using the most cutting-edge web and multimedia design technologies, Cutcliffe said.

Adobe isn't the only competitor Microsoft had to contend with on the RIA front. A small company in Silicon Valley called Laszlo Systems also has a sophisticated tool to build RIAs, and already has made available an open-source version of it, OpenLaszlo, which lets developers build both Flash- and Ajax-based applications.

David Temkin, founder and CTO, of Laszlo Systems, said Microsoft's interest and entry into the RIA space is good for competitors, because it should stir up interest in related products.