Ok ladies and gentleman, this problem of converting mp3 seems to be really popular these days. We already talked about one simple method in this other article, using Winamp. Here is another simple tutorial with few screenshots to help you decode your beloved legal files in order to eventually put them on a cd.

Step number 1
Download and install Audacity. Audacity is an absolutely free audio editor, developed by Mr Dominic Mazzoni, for Windows, Mac OSX and Linux. This software has lot of useful features (we will investigate better all these features in another article), and the most important feature that everyone looking at this page is interested in is..Importing and exporting of file wav, mp3, and others (ogg vorbis for example).
The link for downloading this editor that will help us to convert is here.
Step number 2 (OPTIONAL, IF YOU NEED ALSO TO DO THE OPPOSITE KIND OF CONVERSION WAVtoMP3)
Do you have the Lame Mpeg-1 audio layer 3 encoder installed onto your computer? If the answer is not, proceed here to the mp3 lame encoder download (windows), or here (mac).
Decompress the file downloaded, and put the file called lame_enc.dll (windows) or LameLib (mac) anywhere in your computer. The first time that we will use the Audacity's command EXPORT to MP3, we will be required to indicate the position of this file.

Step number 3 Run Audacity, and within the menu FILE select the command OPEN (ctrl+o)

(the screenshot is taken from an installation localized in Italian language, APRI = OPEN, you learn some basic Italian here too, wow...)

Step number 4 Search and select the file .mp3 that you are going to decode.

Wait for the file being imported...

Enjoy the graphical representation of the audio file...

Step number 5 Again, within the menu FILE select the command EXPORT as WAV, choose the name of the resulting file, press ENTER and...that's all.