I think, this could be done without IIS URL Rewrite module. <httpRedirect>
supports wildcards, so you can configure it this way:
<system.webServer>
<httpRedirect enabled="true">
<add wildcard="/" destination="/menu_1/MainScreen.aspx" />
</httpRedirect>
</system.webServer>
Note that you need to have the "HTTP Redirection" feature enabled on IIS - see HTTP Redirects