It sounds like you want something to automatically fill in the fields and press a button. You can do this by using the Windows SendKeys API. There are various ways to do it with VBScript/PowerShell/AutoHotKey/AutoIt. Pick your poison.
I would probably do it in AutoHotKey because you can have it compile the script as an EXE to hide the username and password it enters.
You can have it search for the Window and focus it: http://www.autohotkey.com/docs/commands/WinActivate.htm
Then send keystrokes and button clicks to it: http://www.autohotkey.com/docs/commands/Send.htm
You can navigate the form by sending they Alt + hotkey of the form field. The hotkeys are normally underlined when you press the alt key on a form. So use this technique to focus the first field, and then either use it again or send the tab key to change focus to other fields. I would suggest avoiding use of tab and use the Alt + hotkey approach to select send input to all fields and to focus the form submission button.