>They'll also need to pass my aspx app information from their application. Is a webservice, as you suggested, the best way to do this?

Well, if the browser has to be visible, no. Web Services are a way of programming that let you call Web pages and functionality on Web servers without using HTML or a Web Browser at all. If that sounds like something your interested in, dig into Web Services.

Its easy to get started, start a new Web Service project in VS.NET, uncomment the HelloWorld sample and run it.