Here are some related links folks may find interesting:-

http://www.computerworld.com/action/article.do?command=viewArticleBasic&articleId=9040318

http://blogs.zdnet.com/microsoft/?p=543

http://blogs.consumerreports.org/electronics/2008/02/vista-to-xp-the.html

http://weblog.infoworld.com/save-xp/

I purchased a new PC at the beginning of the year. I wanted one with XP but was told that they only came with Vista. After 6 hours of frustration the box still failed to communicate with my network so I took it back invoking my customer satisfaction rights. The store ( CompUSA ) was as good as gold and "found" an XP computer "in the back room". Back home unpacked, cabled up, switched on and all up and running in 5 minutes. I will not allow Vista in this office.

If it ain't broke don't fix it. Either that or the Vista installation should come with an initial user option screen:-

Do you want to be treated like a child? Y/N

Click Yes for Vista
Click No for XP