To confirm my earlier response:

EIDE is an extended version of IDE allowing two I/O requests to be proceesed in parallel. There is a primary and a secondary channle and each of the two devices on each channel will be assigned as a master or a slave. If the slower CD-burner is on the same channel as the hard disk, then it can hold up the very traffic needed to feed the burner utility's buffers during a burn.

So the CD-burner should be placed as the secondary master. That should speed operations up and certainly make the chances of succes higher.