Hmm. I put in the DX-33, adjusted the jumpers according to the sticker on the case, but it wasn't stable at all. FreeDOS would not boot ("Bad or missing Command Interpreter"), and my NetBSD boot disk would crash with a white screen when it entered protected mode. It makes me wonder if I got a bad CPU or cache memory, since when I turn the cache off in the BIOS, the machine is stable (though a whole lot slower).
Interestingly, running the CPU at 25 MHz makes it (more) stable, stable enough to boot NetBSD (slowly) or run Windows 95. I'd really like to get 33 MHz going. though.
I was under the impression that 486DX-33s didn't need heat sinks, but I ordered one anyway just to make sure. It still hasn't gotten here yet...damned eBay.