Long term prediction: Microsoft loses its monoply power
The new DRM features of Vista will turn off many users who are more interested in using their computers for information technology than for watching movies and listening to music. Any security advantages of DRM will probably be countered by more problems with interoperability with third party software and other operating systems (dual boot!).
Some pressure for the transition from Windows to open source will be the fear of some foreign governments of security issues with a closed operating system. Several years ago Microsoft had to provide Windows source code to the Chinese government.
Microsoft has been very effective in fighting back against open source using threats of patent infringement and "influencing" government officials. All large corporations "influence" government officials, so I am not particularly picking on Microsoft here. I also acknowledge that Microsoft has a responsibility to their stockholders to make a profit. BTW, I sold my Microsoft stock in 2005 because I was unhappy with their pushing proprietary document formats - not a financial decision.
I believe that in the next five years that more local and national governments will either use more open source software or completely switch over to open source. I expect this to be a slow and steady process. I also believe that organizations not using open source software will eventually find themselves with both economic and technical disadvantages.