Microsoft has a major hole in its Windows 7 strategy. It doesn't support custom-built applications made to run on the company's aging Internet Explorer 6, but now some former employees think they've got a solution.

The startup is named Browsium, and its first product is named UniBrows, which the company says will run those IE6 apps on IE7 or IE8 on Windows 7. UniBrows v1 became generally available Tuesday.

Even today, nearly ten years after its first release, a lot of corporate IT organizations are still supporting internal-facing IE6 applications that are critical to their users, but they lack the resources to replace or rewrite them to run on more "modern" browsers, such as Microsoft's (NASDAQ: MSFT) just-launched IE9.

The fact, however, that many of those customized applications won't run properly or at all on more recent browsers is creating a serious problem for Microsoft.

In places where there are a lot of IE6 applications in use, some of those organizations are putting off upgrading to Windows 7. Besides the fact that those unmigrated users represent money left on the table to Microsoft, it also means those users are, in a way, stuck in the past with a future support nightmare looming.

Microsoft has repeatedly implored users and IT professionals still running Windows XP, which came with IE6, to move forward in order to get the pain over with. That has not been completely convincing, though.

"Since businesses are being forced to move to Windows 7 and IE8 (and soon IE9), they are faced with either bearing the extraordinary cost and time of rewriting those line of business applications, which may not even be practical, or having to use complex and expensive virtualization options," a statement on Browsium's website said.

In fact, even this week, more than 11 percent of users on the Web are still running IE6. Meanwhile, IE8 holds a 35 percent share, and IE7 has 8 percent, according to the latest figures from Web analytics firm Net Applications.

Browsium is located in Redmond, Wash., not far from Microsoft's main campus, and several of those working there are former Microsoft employees.

"UniBrows eliminates all of the pain points for companies who are stuck on IE6, and would love to move to IE8 and Windows 7," Matt Heller, founder and CEO of Browsium, and a developer who worked on IE at Microsoft, said in a statement.

The company claims it has developed a way to handle IE6's quirks that does not use virtualization.

"UniBrows solves [the compatibility] problems via an IE8 add-on that enables IE6 web applications to run in an IE8 tab, enabling enterprises to upgrade PCs to Windows 7 while keeping their legacy IE6 applications running unmodified," the Browsium statement said.

Further, UniBrows is compatible with all IE6 Web applications, and is completely transparent to users.

"UniBrows delivers complete IE6 functionality and behaviors by using the original, native IE6 rendering, JavaScript, ActiveX and security design," the company statement said.

The company will license UniBrows to enterprises with between 5,000 and 50,000 PCs. A sample license would cost a basic $5,000 fee plus $5 per seat.

Stuart J. Johnston is a contributing editor at InternetNews.com, the news service of Internet.com, the network for technology professionals. Follow him on Twitter @stuartj1000.