Maker of the 80 gig? 5400 rpm drive or 7200(not that that makes any difference)? If is an IDE hd doens't make any sense why it cannot be read. Set it as a slave, position 2 on your IDE O cable and see if it recognizes it then. It's a IDE and the ext is USB or SCSI? If the 6 year old puter has usb (which it must) then, yes, it should recognize the drive usb or SCSI. You might want to spec the older mobo so we can do a better eval. by the way, PATA is the older conventin for all IDE drives except for MAC which are all SCSI. Newer drives are Serial= SATA.
Noli Nothis Permittere Te Terere!!
EVGA 680i, Dual EVGA 8800GT'S (650/950), 4 gigs OCZ DDR2 1066, Intel Q9450 at 3.8 Ghz, Koolance Water Cooled, Dual Plextor16x DL DVD+/-RW. Dual WD 250gb 16mb Cache Sata 3.0. 3DMark06 score = 19,168.