See if you can get an LG GE20NU10 or GE20LU10. There is a newer model out, which I don't rate that good.
Also, this is a stupid question, but when you use an external burner, the blank CD being written onto is put in the burner while the CD being copied from is put into the actual computer, right?
Assuming your internal drive has CD writing capabilities, too, then you can do as you like.
On the other hand, it is better (in terms of reliability) to create an image file from the disc you want to copy instead of a disc-to-disc copy.