Automaticall fill and submit

Hi All,
I want to open a web site form, (lets call it signin.php), which has two input boxes (username and Password) and a submit button. I then want to fill in the inputs and click submit from the vb program which opened the form, all without any user input.  The signin script will check the username and password against a database and return either success or fail.
Can anyome point me toward a solution?
 
Thanks
dcroose