This is how ADPassMon opens the Change Password dialog box in OS X.

change_password.scpt

--this first line gets the x in os version 10.x
set osVersion to (do shell script "sw_vers -productVersion | awk -F. '{print $2}'") as integer
tell application "System Preferences"
    try -- this won't work if UI scripting is not enabled
        set current pane to pane id "com.apple.preferences.users"
        activate
        tell application "System Events"
            tell application process "System Preferences"
                if osVersion is less than or equal to 6 then
                    click radio button "Password" of tab group 1 of window "Accounts"
                    click button "Change Password…" of tab group 1 of window "Accounts"
                end if
                if osVersion is greater than 6 then
                    click radio button "Password" of tab group 1 of window "Users & Groups"
                    click button "Change Password…" of tab group 1 of window "Users & Groups"
                end if
            end tell
        end tell
    on error theError
        display dialog theError
    end try
end tell