I'm confused by your original post, do you mean you want to record the sound coming out of your laptop? I.e. what ever is playing out of your speakers, out of your master L/R output you want to record that?
If so, some sound cards have this option when selecting a recording source there is an option to pick the main L/R Mix, or main stereo out etc..(but I'm guessing yours doesn't?)...You could invest in another sound card as suggested, or the only thing I can think of is investigate piping your sound buffer into a record buffer. Can this maybe be done with pulse audio? (pulse n00b here so I don't know!)