A friend asked how to do this.  Since I was curious myself and figured others probably are as well, I've posted it here.

• right click on your web project
• choose "property pages"
• choose "start options"
• change the Server setting from "use default Web server" to "use custom server"
• configure your "Base URL" to the root of your website.
  note: I received an error: "Unable to start debugging on the web server. Logon failure: unknown user name or bad password." when attempting to open a local url using host headers (http://www.me.rentals.com).   Using localhost with a virtual directory worked fine (http://localhost/csi.rentals.web).

Now, when you <F5>, you'll launch your website like we used to in VS 2003. 

If you want to use a host header, I'd look into Internet Options/security settings in Internet explorer (check "automatically log on with current username and password) as well as the user configured for your asp.net application.  Documentation suggests that the debugging user must be an administrator.  I'd use SysInternals RegMon and FileMon to see what access might be failing but this is outside of the scope of what I was trying to accomplish.   Good luck!