Two ways to go about this:

1. Old style - set your SB-600 to SU-4 remote mode, and it will fire whenever it sees the SB-700 going off.

2. AWLS style 1 - set the SB-700 to Commander and the SB-600 to Remote. The corded flash does not really know it it's corded or plugged straight into the camera's hot shoe.

3. AWLS style 2 - if your camera's built-in flash has Commander capabilities, ditch the cord, set it up, and assign SB-700 and SB-600 to remote roles on Group A and B, respectively. If you don't want the built-in to contribute to the exposure, dial it's power to "--", and better yet, get the Nikon IR pannel to cover it.

http://egozarolho.blogspot.com
1. Good content, good aesthetics and good tecnique. On that order.
2. Light is more important than glass and pixels.
3. In the digital photography process, software is as important as gear.