VS 2008 has what I think is a very annoying bug and Redmond thinks is a useful feature. If you create multiple web applications within a single solution, then when you run the solution, by default VS will launch a "Cassini" WebServer for each web application project. The rational Microsoft gives for this being a "by design" feature is that you may want this behavior when, say, debugging a web app that connects to a separate web-hosted WCF service. Sounds reasonable, except there already exists functionality just for this purpose: Solution -> Properties -> Multiple Startup Projects! If I check "Single startup project" here, then under no circumstances should multiple projects start up! This is especially annoying when developing solutions with several web projects - each spins up a little web server icon in the task tray, with an annoying "pop" and balloon telling you where it's running. In addition, each takes up memory and slows down the build-and-run.
I scoured Google and the forums and got nothing on this, but this afternoon I happened on the simple workaround. With a solution explorer and properties window open, select each web application project. In the properties tab, set "Always Start When Debugging" to false. Next time you run, only the projects specified in Startup Projects will be run! Note that this "properties window" is NOT the same as the "Project Properties" that you get to from Project -> Properties.