My own first PC had a 15GB HDD, that was in an eMachines Celeron 633MHz with 64MB of RAM, which I soon upgraded to a whopping 192MB, AND added a GeForce 2MX 32MB PCI card for gaming awesomeness. Got that PC for Christmas in 2000 when I was 13, lasted me a month shy of three years somehow.
My parents PC at the same time had a 12GB HDD (in a Pentium II 400MHz), before that my Mum had a 486 but I've no idea what size the HDD was.
Can't believe 15GB used to be sufficient, these days the OS alone takes up that much.