You will need line outs or a headphone out on the boombox and line in's on the laptop. Then a cable with the right type of connections. The laptop (if it has a line in) will be 1/8' stereo. The boombox could have 2 RCA outs (unlikely) or 1/8' stereo on the headphone jack (most likely).
You will also need some recording software on the laptop.