Lookup

Hi. Not sure if this post fits here, but I hope someone can point me in the right direction. I have a site that contains info for 4 different offices. I am looking for something to where a user can go to www.mysite.com and come to a login/registration page. Upon registering I’d receive an email to activate their account and setup whether they had access to www.mysite.com/a or www.mysite.com/b. I’d like the sub directories and their content to be protected from someone just typing the url without haveing registered. I’ve spent a lot of time testing different CMS scripts and other user management scripts. They all seem to be geared towards pay sites and I haven’t found one that seems to fits my needs very well. If anyone knows of such a script, free or cheap, I’d greatly appreciate it!