Heh...I suddenly remembered the OpenGL patch for Unreal. Reinstalled Unreal from scratch in a different directory, upgraded to v224, installed the OpenGL patch...
...and I'm now running Unreal in glorious 32bit OpenGL at 1600x1200 with all effects turned ON at a silky-smooth framerate.
W00T! W00T!
D3D still runs like a slug on 1024x768 with all effects turned on. If that's not an argument for including OpenGL support for Unreal II, I don't know what is.
I highly recommend anyone with a GeForce card doing this. I've noticed a few glitches in some scenes (and it's not clipping the textures on birds and leaves, giving a black in-fill), but I guess I can live with that. It does it in D3D as well. The detail textures are now sw33t.
Now, if only the links to the S3TC patch files wasn't busted, I could have some serious fun with UT.