OK... So on the same stereo wave form you have recorded 2 different sources. 1.Export into Sound Forge [ctrl+E].
2.Choose the "channel converter" plugin.
3.The preset "stereo to mono-left channel 50%/100%/etc...". [This will take only the info of the left channel and create a MONO file out of it. You might have to adjust certain parameters to get the best gain for the wave without clipping. The 50% setting should be fine but if its too low try experimenting with 100%.]
4.After you have created your mono file of just what you wanted create a open template [of the same sample and bit depth of course] and copy the mono file into it and save to another name.
5. Go back to the other file that you did your stereo to mono processing on and "undo" it. [You'll have your original file there again.]
6. Now do a "stereo to mono" utilizing the "right" channel [50%/100%/etc...]and follow the same steps that I've just outlined.
7. Noise reduction 2.0 is a great plugin to use on any source material that has any unwanted frequencies that must be removed.

Anything else? Later.

How is it done in VV3? Curious...HMMMMM?

In Vegas 3, the audio event properties allow you to choose (among other options) left or right channel only as mono. This takes one channel, centers it, and drops the other channel out.

If you duplicate that event, put it on another track, and choose the opposite channel, you can use both left and right channels simultaneously, and treat them differently if needed.

Ya learn something new every single day!