yes, but you'd have to switch the mic input to line input. (you'd be running approx 3-5 volts out of your computer's headphone jack into a mic connector expecting no more than 10 mv /.01 V)
But it would be in mono, with noise gate, compressor and reverb added... it would sound pretty awful.
Why wouldn't you just split the headphone output from your laptop using a Y cable into 2 1/4" jacks, and then go into the 2 aux ins? Since your laptop output would be headphone level, usually only a few volts hotter than line level (close enough for most purposes, you may have to lower the gain though, via the trim knob)
Mark
