Having a drive as slave on an IDE channel with no master is not "to the book" and may or may not work reliable. After many years of dealing with the PC, I've found that the best setups tend to be as close to plain and to spec as possible. What may work is one thing and "interesting" but not what I'd want to rely on.
80gb Western SATA (sata1)
40gb Western PATA (want to slave it)
MSI MTV6 MoBo (sata controller on board)
AMI Bios 2.0
DVD and CD-Burner on Secondary IDE, (M/S respectfully)
for a while the bios was reconizing the 40gb (slaved on primary ide) then not, then yes, now not. Should the 40gb be mastered on the primary ide? Tried to auto detect the 40 and user defined, same results. Also, anyone know about the converter chip/module that'll plug into PATA and convert the interface to SATA. It would be easier and use sata2.