There are a lot of XP users out there, and some times, it is the only software that works.
For example, Canon has XP drivers for firewire and the 1D MK II / 1DS MK II, etc. They have dropped this support for later software versions, so you cannot use the firewire port to set the personal camera settings, or to tether the cameras and use remote release. There are USB drivers, so you can connect and download images, but some features require the firewire connection. There are lots of peoplle who buy a used MK II only to discover that their nice new 64 bit windows 7 computer can't connect to the firewire port.
For older, unsupported gear, it should be easy enough to get a used < $100 desktop that runs XP. This XP box would serve as an intermediary with a newer computer. Then you are freed up to do your post processing on a computer with a newer OS.
If you freeze all your software to accommodate one dying link in the chain... eventually the chain will break.
I'm just trying to offer practical thoughts on this issue (which I've defintely gone through myself).
Almost always, software provides very affordable workarounds for issues like these. VMWare is a good example.