registering on network site

how does one register on network sites? for the life of me cant get it so folks can register on the network site. they are redirected to the main site signup page. when they create an account, it only gets created on the main site and not the network site (though they can log in)…

have set up the network for allowing users to register and on the network site too (via editing the site and users can register option)…

seems like I must be missing something obvious here as folks running a network site might want users registering on their sites and actually showing up there as a user…

any help would be appreciated…