Not sure about the machine but according to Romero[1] Quake (as with Doom) was developed on NeXTSTEP 3.3, which they continued to use, later running on Intel hardware, until 1996.

QuakeEd on NeXTSTEP: http://rome.ro/uploaded_images/qe_dev-726646.gif

[1] http://rome.ro/2006/12/apple-next-merger-birthday.html

Would that have been running NT back then, perhaps the MIPS version?

The environment does look like Visual C of which 1.0 came out somewhere in the 94-95 time-frame if I'm remembering it correctly, though it might have been just a tad earlier.

I bought one of these machines around that time for a design company I was interning at. It's an Intergraph, obviously I have no idea which model. These machines were built to order, so it could have anything in there. That multimedia keyboard brings back memories, prolly the worst $100 I ever spent.

This machine would be running WinNT 3 or 4, most definitely not the MIPS build.

Probably Intergraph.