Hi,

You said,

I have some large MP3 files which won't fit on a CD for playing in my car.

In that case reduce the amount of files then copy on CD, if you use 700 MB CD-R your data should be under 700 MB. Some software shrink the data.

MP12 suggessts using the backup disk option. Will the files play on my player?

It is not backup that play, it should be the format option you use during burning CD, you have to choose, Playable on home player, car, stero or only on Computer. This option varies on software check yours.

It will much helpful if you also read help file of your software.

I hope in the meantime someone will also answer you.

Thank you

nihon94