What's the difference between BizTalk and .NET Web services? I don't get it.

Microsoft BizTalk Server is an application designed to help you quickly build and deploy business processes internally and with your business partners. It offers a suite of tools and services that can make building business processes and integrating disparate systems much easier. BizTalk can leverage Web services. Here is an article that may help.

A Web service at its simplest is an application that can be accessed and consumed over standard protocols and transports such as HTTP and TCP. Web services are self describing and can be "published" using UDDI so other applications or humans can find them. In truth, there is no thing such as a ".NET Web service", only Web services that are built using .NET and that run in .NET. You can build a Web service in many platforms inclusing J2EE. IBM has included some great Web service tools in their latest IDE, WebSphere Studio Appplication Developer. Web services are based on industry standards which were co-developed by Microsoft, IBM and many others. In fact, one of the great attributes of Web services are that they are platform neutral. What I mean by that is that you can create a Web service and run it in .NET and then consume that Web service in a J2EE application or vice versa.

BizTalk is a product, Web Services are a standard.