You can't. Grab Audacity (audacity.sourceforge.net), set the input to your stereo/mono output of the sound card, and play back the recordings as Audacity records. Trim dead space, and save as either a .wav or mp3.
Next time, just use Audacity to record everything. If you want to record your mic + other people, just make two tracks, one recording your sound card's stereo output and the other record your mic-in.