How does the Nikon SB-700 CLS work with the Nikon D5000?

I know that the D5000 doesn't have a Commander mode, but I'm sure the Nikon SB-700 has a Commander mode? So that will let me use my pop up flash to activate the Nikon SB-700 wirelessly right, but it IS NOT i-TTL? I also have a D70 so it becomes i-TTL when shot wirelessly?

You can use the AB-700 as a remote or "slave" flash as you would using any other dedicated Nikon flash, you just can't control it (changing the output of the flash from full to 1/64th from the camera)

Eventually all your gear will catch up to the technology available at this time. For instance the much older Nikon D300 does have CLS and can use any of those functions.

Had you waited just a little longer and bought the Nikon D5100, you would have the CLS feature.

While the CLS feature is really cool and can help a photographer setup multiple flash units without needing to use a flash meters and adjust each remote flash by visiting each one and taking readings, the photographer can use the CLS feature on the camera and make all those adjustments without needing to leave the tripod holding their camera.

Commander mode on the SB-700 means that the SB-700 can be used to trigger another CLS flash wirelessly.
What you have in mind is an optical slave mode, not commander mode. In case of the SB-700 it's called "SU-4". If it is what i think it may be, then yes, the popup flash of the D5000 should be able to trigger it in manual power output mode wirelessly.

Yes, if the D70 supports CLS and is used in commander mode, then the SB-700 will work with TTL wirelessly with it. You'll likely have to set it to a different slave mode then though.

Off camera TTL is a dodgy thing though, as the camera does not know in which direction the flash is pointed and what part of the subject it illuminates. If it just illuminates a small part of the subject, then that can seriously throw off the TTL metering. Hence i prefer to use off camera flash in manual output anyway.