How secure or reliable does that count need to be? Just sort of an "idea" of how many?
IP addresses are dynamic and change from connection to connection.
Basically, reliable only for the time the person is online at that specific time.
If the download and count is critical, a registered member log-in is the
only way to control those downloads. The next decision is whether or not
to retain the IP address forever? So once an IP address downloads, they cannot
ever download again? Or will you have a time period, like the IP cannot download
again for 24 hours?
These decisions affect the method and scripting you will use.
In any event, you are going to retain the count for each link, so you'll need a
database of some kind ... most likely using PHP and MySQL.
This idea of yours sounds sort of like a voting script where a person can vote
one time for an item (or a link). It retains the number of votes for that item
and also won't let that IP vote again. You can find scripts like that and simply
change the "concept" of the script to your own needs. Instead of "votes", it will
be "downloads".
EDIT:
See if this script (or others on this site), might be something you could use:
http://www.hscripts.com/scripts/php/...ad-manager.php
.