I'm sure it was officially re-released for modern (of the day) PCs before this? I think I've still got it on discs somewhere, a set of the first trilogy, Vice City, and maybe San Andreas.

Your memory is correct! They released GTA1 (all expansions) and GTA2 as free “Rockstar Classics” in 2003 and 2004 respectively: https://web.archive.org/web/20130116055920/https://www.rocks...

One can get those versions here: https://archive.org/details/rockstar-classics_202107

They're great on XP-era machines! I have both installed on my HITACHI FLORA 270HX

Those were GTA3 versions. The linked version is for the original GTA with the classical top view perspective.