I have no idea about if xp will still be supported but just a quick heads up: you can purchase a OEM keys from opiumpulses for windows 7, 8 or 10 pro editions for anything from about €10 up to €20. They have limited stock & the prices fluctuate up & down. I ended up paying about €9 for windows 8.1.
I installed it on both my current laptop after downgrading from windows 10 & on my mac mini on Parallels VM.
You are right, win 7 or 8 can be quite cheap, but I need my XP for other older programs. My favourite game "Riven"(the latest DVD version!!) don't run on win7 (the reaason is this old worse apple quicktime thing...) . And other 3D-tools neither.
But Visionaire runs well on win 7 64 bit, so I have two systems to use, but it's very uncomfortable to switch. XP is my "mother" home system :-) :-) I have tried to build an intranet between xp and win7 - but I failed. I can't stand this user rights bullshit... Win7 don't find XP. It's only possible with ONE file on win7 for exchange all data. Shit!
I hope the 4.3-Visionaire editor has more possibilities (f.e. to delete a line and put it into another part). Thats the most worst thing: to write, delete and insert EVERY block manually twice or maybe 20 times... I have a lot of unused containers for all cases in my games to use the right one I want sometimes ...