password protect my site

I have an educational site that needs password protection Students pay via paypal and return to our site I want YOU to script a user / password login page for acces to a few directories, Maybe validated by the paypal return? not sure I'd like to have access to users to delete them, maybe even track theire traffic. Open to suggestion as to handle returning students cookies re direct to login page ???? whatever Please ask any questions - not too sure the info you'd need. Thanks