Stinger42, once you have over modulated audio - you can't get it back, it is buggered. Sure you could filter out the noise it produces, but there is nothing there but white noise, it has distorted to the point that words and sounds we associate with words are not present.
So your left with cleaning up the audio and that is about it. So what do I do?
Test record before every record! I admit though, I did this for about 40-50 odd shows, after that I started to be able to "hear" if the levels were right. Plus the fact that I use very controlled conditions and everyone knows the level they need and they don't mess with it too much.
In your test record get your attendees to talk at their normal level, get excited as well just so you get that top end taken care of. One trick I use is to hit the record button and don't tell them, it is hard to be natural when you know your being recorded for the purpose for testing levels.
Give yourself plenty of what's referred to as "headroom". That means you need to set the levels low enough so that at someones loudest they don't over-modulate.
Ideally in your test recording you should look at the meter. You should see the levels floating between -7 to -10. That is optimal. But I have rescued levels that were about -35 (that's pretty quiet!). But it also demonstrates an important point.
You can nearly always rescue quiet audio but once it goes +0 your stuffed.
In post production I both run the audio through a compressor and normalize the levels up to about -1 (no higher if you intend to convert the file to an mp3). This brings up the levels from that "safe" -7 -10. So the resultant audio file has a constant loudness and there are no big fluctuations and listeners are not messing with the volume through the show.
I don't use Audacity to edit the show. I use SONY SoundForge. Excellent bit of kit for bugger all outlay. One of the best investments I made. You don't need Audition, it is way too much for the average podcaster.
Ultimately though you have to expect an interview to be an unknown quantity. Your guests may not know as much as you do about audio and it might have been a monumental accomplishment for them to just get on Skype! I think that listeners know this and accept that an interview may not be the usual top quality and why. But with a bit of experimentation, a test record and slick editing you can make the most of the opportunity.
Hope that is the sort of answer you were after. Cheers and great question! Maybe I should blog this stuff?