I have a cd-rw with some files on it. I will need to add files on it from time to time. How do you add files to a cd-rw without erasing the old files on the disc?
It's called multisession.
Nero for example will allow you to multisession.
Nero's INCD (not recommended) or Roxio's DragtoDisk (preferred) would work fine.
Or just get a USB flash drive.