You can only have two devices on the IDE (PATA) channel. You probably have two channels so you can have a maximum of four devices, but your hard drive must be included in the total. If you want more devices, you would need to do it by other means.
Don't confuse power with the IDE ribbon cable. The power is from those four wire Molex connectors that come from the power supply. You can get Y connectors to add more power plugs.
You could get external drives or put regular burners in external cases. You could get a PCI to IDE board.
In either case, check the appropriate threads about good external cases and good PCI to IDE controller boards.