In short, buy windows vista, if you do NOT play video games, or watch dvds, or play cds on your computer.
if you do, then stay as far away from vista as possible.

The following article link was posted on an IT pro website, the content is solely the work of the person that owns the site it is hosted at.

http://www.cs.auckland.ac.nz/~pgut001/pubs/vista_cost.txt