How to change the password in windows without knowing the current password?

Hey guys
I want to change some password of any pc with out knowing their current password.
i know of using command prompt
using net users..

but is there any other way to change the password using some other technique?

i don't know proper but one of my friend changed my password using regedit...
and i know we can do this after some one had login but is there any way to change without log in.

btw i am using win 7.

thanks in advance

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UPDATE:

First we will look at the link which u have given.....

all the links had one similar situation which is.... they are trying to logged in to the pc

ok?

In my situation, the PC is already logged into, and a password is not required for login. This can happen if I am Administrator or not a limited user by using "net users" command from CMD.

And this I guess you know. Right?

So tell me now how this question is similar to links which you have given?