today I bought an iMac 20" 2.16 c2d for $700 which I thought was a good deal but it came with no install discs and the guy did not know the user name or pw... Can I use my aluminum iMac install discs or to they have to be the ones that came with the system. When I try to install leopard it just shows 1 big lock and a section for the pw. Any help?