Assuming you have the right to duplicate content on an audio or data CD and have a supported CD burner, there are several methods you can use.

Audio

If you have both a supported burner and a separate CD-ROM drive and want to burn a copy of an audio CD, just mount the CD and drag its WAV files directly into the burn window.
If you just have a burner, use it to mount the audio CD and drag its WAV files into the Tracker. Unmount the disk, insert a blank, and drag the files from the Tracker into the burn window. In either case, be careful to preserve the track order!

Data

To burn a copy of a data CD, you’ll need to create an image file of the disc’s contents first. Mount the CD, open a Terminal, and type df. You’ll see volume names along with raw device paths. For example:

/some_disc hfs 15644 826 -AM-PR- /dev/disk/scsi/0/3/0/0_1 

Copy the appropriate device path to the clipboard, then use the „dd“ command, with something like:

dd if=/dev/disk/scsi/0/3/0/0_1 of=image.img bs=1024 

You won’t see anything for a long time. The prompt will be returned when the image file is complete. Now, in CDBurner, pull down Disc | Add Data Track, navigate to image.img, and burn.
Note: You’ll probably find that tools like WriteCD and Melt (both on BeBits) make this process somewhat easier, but that depends on you…