lost password

i had bought 3 hp compaq dc5100 desk tops one had the password taped on one of the pcs but the guy that had cleaned them up threw the tape away that had the admin password on it we have pass word recover disc and i can not get it to boot to the disc you log on it comes up windows xp and has a name on it and is asking for a password want to safe mode is doing the same thing im thinking these desktops were on a network can anyone help me