HOLY CRAP… 80GB! WOOT!
Anyways… With that kind of a computer, the hd’s arent going to matter much as far as speed. Just get some cheap one, it should be fine. Your going to need a ATA hd, ata 100 or 133 would work, it dosent matter. Basically, you can get just about ANY hd as long as it dosent say SATA on it. And no, cant have more than 2hd’s on your comp. Your going to need to swap out the 20gb one and transfer the files…
HD’s are cheap as hell, just get a 250 or something 