Toast 3.5.x
Since the retail versions of Toast 3.5.x only support SCSI based CDR / CDRW drives, you can burn when booted with extensions off (shift key boot) as long as the source data is on a hard drive. You cannot copy information from the standard CD or DVD drive in the Mac since the Apple CD/DVD driver doesn't load with extensions off.

Toast Deluxe 4.1.2 and Toast 5 Titanium
These versions of Toast support SCSI, IDE, Firewire, and USB based CDR / CDRW drives. If you're burning to a SCSI or IDE based CDR / CDRW drive, then you can burn when booted with extensions off (shift key boot) as long as the source data is on a hard drive. You cannot copy information from the standard CD or DVD drive in the Mac since the Apple CD/DVD driver doesn't load with extensions off. Choosing the Mac OS Base set of extensions in the extension manager would provide access to your built in CD/DVD drive and also allow you to burn.
If you're burning to a USB or Firewire based CDR / CDRW, however, then you will need to be running Mac OS 8.6 or later and you will need to enable either the "Toast USB Support" or the "Toast Firewire Support" extension in addition to the Mac OS Base set of extensions in the extension manager.