It's covered in the summary, honestly. Just look up alternate executables for quake 2. Maybe even enhanced engines. Hopefully, Giex mod will work fine under those.
The Steam version of Quake 2 might have issues with mods. I've seen this with the Steam executables for various iD Software games. There are community-made alternative executables for just about every iD Software game.
Your saves should be fine if you change executables mid-way, but I can't speak for every community-made executable.
I found a link to Rich's quake 2 executable. Just scroll down to where it says " R1Q2 b7587" (as of this writing) and that download link should work fine. I downloaded it and successfully opened giex mod when I wrote this.
