I was about to try to also with my D50 and Aperure 2.0 One thing I did try was tethered shooting using Image Capture. The Leopard version of Image capture seems to work with my D50 just fine. It is very limited in that the only control is "take a picture" but it works. You might try that.
My camera is sitting on the same table as the computer. I just need to get the time to try it out. I'm optimistic that it will work because I'd bet Aperture and Image capture use the same underlaying feature in Leopard to control the camera.
Are you still on Tiger? If so that could explain it. Aperture does not pick up some of it's new features untill you run it on Leopard