from memory, as I had similar problems while setting up mine:
set mediator to nommu with medconfig and Voodoo mem to 8mb. Also set mem window jumper on the Mediator board at 8mb if you don't have a pcmcia card attached, otherwise stick to 4mb window, but 4mb is much slower. Also, it's important to set the WB WarpOS prefs correctly, but I can't recall the values. I'm sure you'll find them if you search here in the forums. Finally, make sure you've installed latest WarpUP and Warp 3D and the newest Mediator updates. You'll pretty much now you're ok if you can run ALL warp3d demos (gears 68k/ppc, gl sokoban etc) correctly.
Good luck!