can i "subtract" one waveform from another?

[kristen]

i was recording a conference call on track 1.
it was getting long so I stopped recording on track 1 and went to the next track to continue recording.
I forgot to mute the first track while the second track was recording so the second track is "mixed in" with the first track.
Is it possible to take a copy of the first track and "subtract" it from the second track ... leaving only the second track by itself?

thanks
superkristen