What OS would I be running in the VM? I still can't run Steam on the old OS, and thus can't install/run the respective game I'd want to play :( Actually, now that I think about it, I bet a pretty noteworthy % of my Steam library is literally not playable on any OS supported officially by Steam...
I'm pretty sure you have a few options - you can download an old version of Steam and just not update, you can download the games for offline use and then copy them to the VM, you can just download a crack for that game since any game old enough to not be usable on a new OS wouldn't have DRM, or you can pirate them (as you said). :)