Recovering windows admin password

My friends brother had changed his administrator password and deleted remaining accounts he came to me for a solutions. Then we had googled for some time and finally arrived at a successful solution.
We can easily hack a system if the system does not set administrator password already or we have access to other account with administrator privileges in the system(using Netuser username password).
But how to know a system password when we don't have these privileges. The option is OPHCRACK we can down load this from  the below link for free
http://ophcrack.sourceforge.net/ .
It is a free windows password cracker we can download it by                                                               clicking ophcrack live cd tab.
If the system does not have CD drive  then we can boot from pen drive using this pendrive linux software we can get it from the below link for free of cost.
http://www.pendrivelinux.com/creating-a-bootable-usb-ophcrack/