You can still buy Thief, Thief Gold and Thief 2 from various outlets and you can certainly get it working on a modern win32 platform judging from the responses on the game's forums. But it's a brittle process with no guarantees (as I know only too well) and only getting worse with time.

GOG might well come out with a version and I'd be ecstatic if they made a bundle which could run predictably on a modern platform. It would certainly save me a bunch of work :)