LisaM221:I have the d300 and sb800 and use the built-in flash in commander mode to fire my 800. What I do is set the built-in flash at it's lowest setting, which I think is 1/128. This usually makes the built-in flash so low that it doesn't have any real effect on the exposure, so all your light is coming from the 800. It works pretty most of the time, but I do still get that little pinlight catchlight sometimes.
I'd like to see if anyone else has any other tips on using the flash this way.
Lisa,
Are you using the SB-800 in SU-4 mode? (Basically a dumb slave.) If so you need to explore iTTL operation of the flash. Using iTTL you can tell the on-board flash how much (if any) to contribute to the overall flash. If no, then there should be NO output from the on-camera flash. You do have to deal with the pre-flashes and that can cause some people to blink, but if that becomes a problem you can pre-set the flash by using the AE lock button.
Ok. Just read your exchange with Moose. Sounds like you are on the right track.