Creating and enforcing a subscription-based service?

I'm trying to figure out an approach to a general idea/problem I have, and
I'm not sure where the best place to start is. There's nothing done right
now, other than paper drawings on concepts, and I'm looking to make sure I'm
using the right tools and a decent approach. Why post here? I've got a vague
idea that I want to involve ASP.NET and web services, etc.

What I'm considering is creating a "widget" - maybe a Java applet, maybe
just Javascript (again ... tools/technology not yet decided) that will
display on a web page and consume a "service" that I will set up. For
discussion, let's say it's stock information. What I want to do is have
people subscribe to the service and field it on a number of screens in their
lobby, breakrooms, etc. Think of it as per seat licensing.

What I'm wanting to do is figure out an approach where I can license Client
A for 5 machines and Client B for 50 machines, and set it up so that Client
A can make the info available to his machines simply by setting up a web
page -- ideally, he need not go to the machine to do anything in particular
(say the machine is in Newark and he's in St.Louis). So if Client A puts an
extra machine on the system and it tries to get the information, I want to
know about it.

Same thing in scale for Client B.

What would be even more useful is having some way of determining that a new
Badguy C manages to scoop information off the machine in Newark, and finds
something that points to the service, and tries to set up a new machine
using Client A's information. I'd like to know about that, too, and be able
to let Client A know.

I'm not so much worried about how much backend stuff I'd have to set up to
manage this, and I can add databases, etc. to implement things. What I'm not
clear on is what sort of an approach I could take that would enable the
"hands off" setup and license/access management for a set of clients so that
they can use the service within their licensed limits, and how to identify
the users (i.e. individual machines belonging to a licensed client) of the
system so that I can try to ensure that the system is used only by licensed

Is this something that ASP.NET can help with, or am I looking at my problem
the wrong way? Any comments on this approach would be appreciated. I'm very
new at ASP.NET, having done a little fiddling with ASP in the past and a bit
of playing with the new Express stuff now available from Microsoft.