I have a DVD of a music concert. Can the audio only (not the video) be burned to a CDR to play on a CD player?
Sure. Lots of ways to do this. Personally I would convert the DVD to DIVX(or AVI) format(google it, lots of free tools) then convert the DIVX/AVI to MP3 using "Media Converter SA"(the downloaded one, not the online one) also free.
There are other programs which can demux the audio out but since DVDs are multiple files, it's easier to convert it to one single Divx or AVI then get the audio out of that.
First you need to rip the DVD. Get a program called HandBrake. I can't remember if that does audio stream only, but if it doesn't just tell it to convert your DVD to a movie file, streaming the audio straight through with no conversion.
Then install the free Virtual Dub and open the movie in it. This program has an option to strip your audio off into a WAV file for later conversion by iTunes or such, or straight into another format like MP3 if you have the appropriate filters installed.