restricting files

Hi, I wish to restrict access to a dir of files, depending on if the user is a logged in and validated member. My first guess was to restrict access to the files with .htaccess, only allowing access if the referring (linking) script was something like members.php, so they'd only get the link if they were logged in, and only be able to access the file via the members page, which required login... but I can't find any documentation for this (perhaps it's not possible), so I need to look at other options. I know I can hide the LINK from non-members, but what's to stop them telling their friends what the URL is? Any suggestions welcome :) Justin