so there is but it is
http://www.google.com/microsoft
Silly me they are all listed at the botom of the advanced search page
Apple Macintosh - Search for all things Mac
BSD Unix - Search web pages about the BSD operating system
Linux - Search all penguin-friendly pages
Microsoft - Search Microsoft-related pages
U.S. Government - Search all .gov and .mil sites
Universities: Stanford, Brown, BYU, & more - Narrow your search to a specific school's website