I have quite a big solution here with a lot of different web applications and sites, around 10-15 of them.
When I attach VS2008 to any process (most likely Nunit.ex
I think what you want to do is set the "Always start when debugging" property to "false" for each of your website projects. Just click the project in the solution explorer, hit F4, and it's the first property in the list.
This property is annoying because even when you attach a debugger to IIS (i.e. you're not even building the solution), the little servers start automatically.