Can someone help me out.

I have a number of old MP3 and RealAudio files that I have downloaded from public sites (The Smithsonian, Max Hunter, etc.) that I would like to put on an audio CD. This allows me to learn them on my daily commute. My problem is that when I try to write them to CD using MusicMatch, CDCreator, or other software I get error messages saying the file format is incompatible. I know that many of the recordings are in mono, or at a compression rate below 128kbit or 44KHz (whatever those are).

Can someone explain to me why I can't write these to an audio file? This is true even after I convert them to .WAV format. It seems that if I want to write a lower quality file to disk I should be able to.

Is there conversion software that is available at a reasonable price that can fix the files so they can be written to an audio CD?

Thanks JAB