i finally installed a multisite version locally on my imac via MAMP. i changed my localhost to port "80" and the multisite-installation worked fine. when i login to wordpress i can navigate through the main site (dashboard and site) with no problem (i also see the "my sites" menu at the top)...
example: http://localhost/wordpress/wp-admin/ -->works fine!
but when i try to go to my subsite (subdirectory) the site shows "not found" for both front- and backend!!!
example: http://localhost/wordpress/subsite/wp-admin -->not found!! :-(
thanks and cheers,
Jochen from Germany