Hello wouanagaine - can I congratulate you on the excellent SC4 Terraformer, as a first time user of the program, it is really great.
Anyway, re Windows Vista, I can confirm that SC4 Terraformer DOES work on Windows Vista (I'm using Home Premium Edition).
To do this, I extracted the v1.1 file as normal, right clicked "SC4 Terrafomer.exe", and on the Compatibility Tab I told Windows to use compatibility mode for Windows XP SP2, and to run in Administrator mode. I don't know if you have to do this, but as the program has been designed for XP it seemed to be the right thing to do.
As far as I can tell, all the functonality works correctly.
(PS: SC4 Mapper does not work under Vista, even with the compatibility stuff above enabled).
I hope this is helpful, and many thanks,
IAP