if you have a digital in on your soundcard you should be good to go. then you can burn the discs on your g4 (that is a MAC, right?).
I recommend using a computer based burner as you will be able to fully edit the music once its off the DAT. you can add fades at the beginnings and ends of sets, you can split the sets into tracks, and you can also repair any digi-noise, clicks, or pops that may be on the dats.
Good luck.