Submitting Forms

I have an asp page with a form on it, the corm contains some list boxes that populate depending on a previous listbox choice.

for example, list box 1 is populated from a database, and user makes a chooice, form is submitted to it's self, and listbox 2 is populated from database, dependant on coice in listbox 1.

fair enough, that works a treat. but to get this working I have used the <form action = "this_page.asp" > tag, and in the first listbox, I use
<select name="F_12025" size="1" id="F_12025" onchange="products.submit()">

my problem is as follows, at a certain point, the user has completed the form and must click the submit button, to sent the form to a thirdparty dll.

I cannot find a way to submit the form to a different page than is speccified in the form tag, (in this case not a page, but a dll, but what's in a name eh?)