I ran across a need for a stand alone IE6 because I have installed IE7 at work but I need to test against IE6 because that is our corporate standard.  The only issues I have found with the stand alone are it doesn’t seem to register cookies correctly and the bookmarks don’t work but as long as you can get to your page for testing this should get the job done.  I just with Microsoft would pick a standard CSS, but because they don’t web pages will render differently on all versions of IE.  It will be nice to see IE8 as it looks like that passes the ACID test so it will render similar to FireFox.