I finally got the extruder to grip the filament. I Dremeled some ratchet steps into the stepper's shaft, and now it will extrude thread out of the nozzle at about 25mm/minute. It can do 40mm/min, but it slips a lot then.
It extrudes, sort of. I can get it to go for a few minutes, but then it stops. I tried making the test part, but when the head stays in one place too long, it starts slipping, and then won't extrude again until I push the filament down for a bit. I'll have to play with the Reprap software settings. It's also slow as molasses. It didn't even finish a layer when I let it run for 4 hours.