The user of Derive Genres who reported the Calibre 2.2.0 issue to me in the first place discovered it while using a Mac.
As for free XP replacements without buying a new pc:
As for keeping XP but running Calibre 2.2.0 within an Ubuntu virtual machine inside of XP:
http://www.psychocats.net/ubuntu/virtualbox
And for those who have or can get a new or used ChromeBook very cheaply, you can install a full fledged Linux on the Chromebook hardware using
https://github.com/dnschneid/crouton
Craigslist has old PCs for $50 that can be reformatted to run Ubuntu and used as a Calibre 2.2+ device.
http://sfbay.craigslist.org/search/sys?maxAsk=50
There are almost always options, although granted that they require some effort.
So, I am sanguine about where Derive Genres and my other 2 plugins are positioned viz a viz Calibre 1.48.