Query for adding new user in Windows 2K

Actually I have to modify "Set Password" dialog. This
dialog appear when u press "Set Password" button on "Users
and Passwords" applet of Control Panel. But after
investigation i found that we can't do this.

So we have decided to Create new Control Panel item with
same functionality as "Users and Passwords" with one and
only change of our customise "Set Password" dialog. So we
have to provide same functionality of for adding new user
when someone press "Add" button.

So my question is i have to write code that will call same
API/Function which was called by Standard Windows program.
Pls. U or any friend of u, have any information then tell
me.