If it is an enterprise site, ask in the comments for an enterprise developer license when you order a new license.
Try an iisreset after you've stopped the other ones. I misunderstood your question at first.
I like using this XP Pro IIS Admin for switching between sites. You can get it here: http://www.jetstat.com/iisadmin/
I've never had that problem while using XP Pro IIS Admin.
I keep running into licensing conflicts when developing locally, what is the recommended way for doing this?