An Introduction to the Web Services Architecture and Its Specifications
Felipe Cabrera, Chris Kurt and Don Box have an update to the white paper on Web Services Architecture at http://msdn.microsoft.com/library/default.asp?url=/library/en-us/dnwebsrv/html/introWSA.asp
There are two paragraphs that talk about transactions in the web services world: "Designated Coordinators" and "Long Duration Activities".
