From the install CD, launch Disk Utility. It is available from the first menu in the installer, I just can't remember the menu name.
If Disk Utility can see it maybe you can learn something there. If not the only thing I can think of is to ask, is the hard drive a SCSI connected via a SCSI card? I had an issue like that where the SCSI drive was not seen, but the IDE's were.
Primer (in case you need it):
SCSI (Small computer system interface) were prevailent in Macs until recent years. You can still connect them via SCSI PCI cards and I have seen many of them in Macs. OS X doesn't support SCSI as well as they could, so some problems arise. IDE hard drives are cheaper and are now used in Macs (and PC's).