musteriuz: Indeed - I did download, install and try to run the 64-bit version, but it was a no-go.
X-com: Yeah, gog must have tested it with Vista but it didn't work so Vista's not listed in the compatible OS on the game page. Also I used to use Vista and could get 32 bit software working as well as 64 bit, it only doesn't work the other way around, as in installing 64 bit on a 32 bit system. Most stuff worked but I guess Unity came long after Vista was current so a lot of those programs are hit or miss.
I took what you said as a suggestion, downloaded the 32bit version, installed, launched - and it started! I could adjust graphic and sound options and got to the character select screen, but quit then. All that remains is to try and play and see how it goes. Thanks, bud!
edit: No, I'm out of luck - it crashes as soon as I launch the first mission.