Windows Authentication from non-trusted domain request

[M3Fan]

I'm building a VB.net application which sends an HTTP request to a web form (created in classic ASP) on a remote server. I pass in several form parmeters as if they came from the actual form. The form returns an Excel spreadsheet which I stream into a file. The code works great if the called form is protected via IIS Basic Authentication. However, the form is actually using Windows Authentication in IIS. Hitting the site manually is no problem. I am prompted to enter my name/password, I do, and I go right in. I'm having a real tough time doing this programatically as I am clearly on a different domain than the called server is. I'm assuming this is why I am prompted for name/password when I log in manually to the site. I'm asking this forum because you guys seem to have the authentication knowledge down.