Download File Routine

I have a simple form to validate a user with a password which then brings up another page that show the file that can be downloaded. I have the name of the file hyperlinked. However, that will reveal the specific location of the file to be downloaded. How can I do it so that ... 1. even if the location of the file is known, it can not be downloaded without having gone through the authentication page 2. through a function, download the file. Thanks in advance George