Need some good ideas

Here's one that's got me a little stumped...

I want to be able to filter my network traffic to one remote site. If someone tries to access any resources at this site, I want to force authentication on my NT domain just to make sure they are a valid user. (It sounds pretty dumb but it will appease the person on the other end) I'd like to cover all ways to connect...not just http and ftp. I don't care about traffic anywhere else so I don't want that traffic impeded. Anybody have any ideas?? I've been looking at some proxy packages but a lot seem mainly concerned with only http and ftp. Would MS proxy server be able to do what I'm looking for?? Thanks in advance!

Jim