Yep, you'll need an IDE cable with 3 connectors.
Install the one end connector(that has the greatest distance between it and the next connector) to the MB, install the other end connector to the hard drive(jumpered as Master), and install the middle connector to the DVD-ROM drive(jumpered as Slave).
The hard drive should install ok in the empty bay as long as it's for a 3.25" drive. But make sure you either already have the required mounting hardware or that it comes with the HD. If not, then a local shop may be able to supply what's needed.
And finally, PB was known to be somewhat proprietary with their design, meaning that what should be possible with new hardware installation may not be the case at all.