To the Line In on you laptop?? Use RCA to whatever size your Line In port is, probably 1/8" Come off the Tape Out or 2T REC. Come back in through the 2T RTN from you laptop's Line Out.
Assuming you don't have an external audio interface, Chili is probably right:
Get a stereo RCA-to-1/8" cable (male-to-male like the kind that come with portable DVD players) and run that from 2T REC to your computer's "line in" or "mic" jack. You'd need an identical cable to go from your headphones/line out back into the 2T RTN.