<p>I'm using Visual Studio 2008 to develop ASP.NET applications. Currently I'm debugging with running on IIS. I would like to switch to the development web server (Cassini) for debugging, so that I can use features like edit and continue. The reason that I'm not, is because the development web server only starts up when you are in debug mode. Is there any way to keep it running all the time, and just have Visual Studio attach to the existing server process like it does with IIS?</p>

Once started, the built-in web server continues executing even when you stop debugging, as long as your VS2008 project is still open.  Just start up the debugger when you want to start debugging again.  I typically have another browser window open and interact with the built-in web server from there instead of the browser window that it opens so I can keep working with the application in the same state even after turning off the debugger (which closes the opened browser window).
I'm running VS2008 on Windows XP SP3.