The bios should handled it ok, I think(?). BUT why not set the h/d as master and the cd rom as slave. In which case you are bound to get the h/d as C. If he is concerned about speed of the bootable drive with two devices on the saame ide cable he'll not notice any difference setting it as slave. I am curios as to why he wouild want to do it this way. Making the h/d master, which normally contains much more data would allow him to access the data quicker.