handling downloads with php
i have a site which has downloads for registered users.
now, since i don't have extremely much bandwidth (running the server on my computer) i would like to create some kind of system, which demands for the users to stay in line until the downloads in progress are complete. my question is: is there any way that i can see when the download is complete, so that the server can update their place in line, and eventually let them download the file?
any help is appreciated.