LunaTech,
 
certainly, RX3 is "The" software to do this work but, after Sonar X3 and Melodyne Editor, my budget are low to spend more US$349, for the basic version; the advanced is US$1,199!
 
Thanks for the reply!

EQ will help a lot. If size is a problem export at 16 bits and 44.1 Khz. You can also use double layer DVDs. 
 
 

I was using the spectral tools in audition for this, but I find myself using R-mix more.  Audition gives me slightly better results, but R-mix is a quicker workflow.  I don't have editor, but would be curious about the results.

Melodyne, as stated, is entirely useless for this task. It was made for something else entirely so don't even bother with it. EQ and gating are your best option if you don't own RX3 or the Waves noise series. Cutting by hand is probably going to be better than gating but obviously it's more work. If your background noise is very static you could try snipping some and running it in opposite phase to the source. It'll probably be hard to get a decent loop of the noise but the result might still be better than not doing it, depending on how bad it is. Not sure it's worth the hassle though since you say you were planning on quick and simple.

John,
 
the goal is to put all the 40 files (more than 60 hours of lectures) in a 4.7GB DVD.  This project will be a part of an audio book and the autors need to save money, so that, double layer DVDs aren't an option, they're still expensive here...  I've already received the files in MP3 format and it's going to be the final format, otherwise, they woudn't fit on the DVD.
 
Thanks!

dubdisciple,
 
yesterday, I tried Melodyne Editor to do the job.  First, I converted the mp3 to wav, than to mono and opened in Melodyne Stand-Alone 64bit. The file loaded fastly but the program detection was endless as the file has more than 1 hour, so I closed the program without finishing the detection. Then, I cut a sample of 5 minutes from the file to see if I could get the detection to run. I chose the automatic algorithm and the program seemed to detect the frequencies in separate blobs. I need to familiarize more with the program to make more tests but, in thesis, Melodyne could do the job depending on the size of the file and the machine you have...
Anyway, I discarded using Melodyne to this project, I think I have a decent machine but it seems that it'll explode during Melodyne use...
Later, I'm going to get into Scott's Power book to understand how to use R-Mix to give a try. I'll let you know if I can get any results...
 
Thanks!

For an overview of basic R-Mix operation check out the video here

Sanderxpander,
 
maybe Melodyne can do the job but, as I stated above, for long files it gets too much of the machine making it almost impossible to work.  Could you give me a more detailed explanation how to do the phase thing?
 
Thanks!

Hi, Scook, thanks for the input.

Atsuko,  even though the thought intrigues me and it would make me more eager to upgrade to Editor, I just don't think Melodyne is the right tool fr such a thing. One plus for using R-mix or the other suggestions is that, if the files were recorded under similar circumstances, once you process one, you have a preset that can be copied for all of them.