Knowing Who Is Logged Into Any Particular Workstation?

I'm developing an intranet site that will require knowing who is accessing the site. Since all of my users are using a WIndows domain, I figured I could cut the necessity to log into the intanet site if I could identify each user based on who is logged into the workstation being used to access it. So I figured I would need some Microsoft-specific tech to get this done.

Is something like this even possible? I figure ASP .NET would be my best hope, but seeing that I've never programmed for a Microsoft environment, I would need some coaching. Here's how I thought this could be accomplished (I may need some help filling in the details):determine the IP of the machine accessing the sitedetermine which machine on the network currently has that IPask Active Directory who is currently logged into that machineI don't know that this is possible in this manner, though. Anyone accomplish something like this before? I would think so as it seems like something a lot of developers would want for web applications.