I installed IIS7 beta 3 through Web Platfrom Installer, when I try to connect to it from Internet Information Services (IIS) 7 Manager, I get the following error message:
could not load file or assembly microsoft.web.administration...
Edit: I am running XP SP3 and I do not have IIS 5.
From your question it appears that you are looking for ways to configure IIS Express. As Kat implies, IIS Express doesn't ship IIS Manager like tool (unfortunately).
One way to configure IIS Express short of editing configuration file directly is to use command line tool appcmd.exe that can be found in installation directory of IIS Express.(http://stackoverflow.com/questions/4690358/iisexpress-user-interface)