How To Reset A Login Password?

I am not understanding that in what perspective you are asking about login password.
But if we consider about the login password in an operating system, then there is a simple way to change it. In windows XP go to the control panel through the start menu.
There is an option named 'user accounts'.Click on this, and then you will see all the users of that system there, if you are an administrator of that system. Otherwise only your account will be displayed on this panel. Click on your account name.

All the account modification options that you are privileged with are displayed there like, change my name, change my password, change my picture etc.These options depend on the account type .if you have administrator account then these options may differ from those who have a guest account.

Click on the option 'change my password'.It will prompt you to enter old password (if any) and enter new password.After changing or creating a password, you will be prompt for a password every time you login to the system.In the case of network, the user accounts are created and managed at server (in the case of client/server network).Thus any user account name and password are set by the network administrator.