Looks like it’s possible to install Vista on that tiny little Eee PC. Why? Because you can, of course.
Paul O’Brien figured out the trick to this hack. The key is to make the WinSXS directory a junction (Vista’s name for a symbolic link) to an external SD card. This directory takes up about 1.5GB of space which you just don’t have an excess of on the Eee PC.
You’ll want to grab the largest SD card you can get your hands on. In addition to accommodating the WinSXS directory, it can be used for the program files directory of any additional applications you want to install. Oh, and remember not to remove the drive with the machine running.
Installing Vista on the Eee PC – Link