Authenticated Access in iis6

[Tarvis123]

I am trying to set up a local website, that is also available from the outside using an external IP address, that should only be allowed to be opened up by certain individuals within my company's domain. Right now the server is located on the FTP server of our domain,

I believe I have been finally able to lock out users that aren't supposed to be able to view the page, by disabling anonymous access and checking only "Digest authentication for Window domain servers" and "basic authentication". However, this presents a new problem, as every time you browse to a new page or load a page with multiple images, it makes you authenticate multiple times, which is very annoying.

Am I missing something here, or is there a better way to do this?