Let's look at both the D60 and SB-600 to understand what it can or cannot do:
D50, D40/x, D60
- does not have commander mode for CLS
- has pop-up flash
D70/s, D80, D90, D200, D300, D700
- has commander mode for CLS
- has pop up flash
SB-600
- does not have commander mode for CLS
- able to work as a CLS slave
- does not have SU-4 optical slave trigger mode
SB-800 / SB-900
- has commander mode for CLS
- has SU-4 optical trigger mode
Based on the above, the D60 is unable to trigger the SB-600 wirelessly in anyway. the CLS commander mode can control other CLS flashes, so if you buy a SB-800 or SB-900 and mount it on yoru D60, you can now trigger your SB-600 wirelessly as a CLS slave with the SB-800 as master.
However, the D70/s category of cameras has the commander mode and is able to trigger the SB-600 wirelessly via the built-in onboard camera pop-up flash.
Because the SB-600 does not have the SU-4 optical slave trigger mode, you cannot use your pop-up flash to optically trigger your SB-600.