I have a used iMac running Tiger (X 10.4.9) I purchased a used imac without a password. I have been told to purchase an OS disk to re-set the password. Should it be tiger or leopard? If I use the new OS disk to re-set the password, will I lose installed software? The seller was the spouse of an upset divorced husband and he has refused to supply the password to her, so she can't get it to me.