There is no practical way to connect it without other equipment:
You need an inverter to power it. An inverter converts 12 volts DC into 120 volts AC (house current). You'll need one big enough to power the speakers.
You'd need a LOC (Line-Out Converter) to tap off of the speaker wires to convert the high-level speaker signal to low-level signal for the input to the speakers.
Even after doing all of this, the sound quality won't be anything near what it sounds like coming from the computer - guaranteed!
Of course you can, it is not going to sound that good though, like a subwoofer with an amplifier powering it would. Just attach the speaker wire to the speaker input, then play the music. I highly recommend using normal car speakers though.