Microsoft Netherlands released the information in a blog post that was celebrating Windows 7's first birthday. At the time of writing, the blog post (via winrumors) was still available. Microsoft has yet to take it down, but in case it does, we took a screenshot of the Google Translate version:
In case you can't see the image, the translated text is as follows: "Furthermore, Microsoft is of course the next version of Windows. But it will take about two years before "Windows 8 'on the market." Microsoft is of course refusing to comment on the information and the company's American blog posts celebrating Windows 7's anniversary do not mention Windows 8 at all. Sometime next year we will hopefully see an official announcement, followed by beta versions of the new OS.