If you have IIS Installed, there's a VBScript installed which does just that. I think you may be able to do an ExecWait on it (or a customized version of the script - i.e. write your own and extract it from your install to execute).
I have IIS 5.1, it's in InetPub/AdminScripts and it is called MkWebDir.vbs
(there are a few other useful scripts in that folder).
Hope that helps get you started.