There is a trend out there where people are taking perfectly good machines running Windows Vista and then uninstalling it in order to install the venerable Windows XP.  This process hasn't had a name up until now but I think I have come up with a good term for it : Devistafication. 

Here is how I would define it:

de-vis'ta-fy:
tr.v. de-vis'ta-fied, de-vis'ta-fy-ing, de-vis'ta-fies
The act of removing Windows Vista from a computer and then installing a different operating system, such as Windows XP.

de-vis'ta-fi-ca-tion  n
de-vis'ta-fi-er  n

I hope this helps to ease the language burden often associated with this task 🙂