Auth Pass Values to IIS

Hi,
I am trying to create a custom login page for Outlook Web Access 2000, and want to have a form that asks for Username, Password, Domain. Is it possible to pass the form results to IIS for authentication? CUrrently IIS pops up a window prompting for these and it is confusing to new end users.

If the Outlook user accounts use the same directory server that IIS uses, I think authentication dialog won't popup anymore.

That is correct, however the OWA users dont have assigned workstations on our network. They work out of different offices in different domains. So I want them to enter in their info.