Capture the IP Address and current date and time (in UNIX Timestamp format)... Store that in a DB or FlatFile.
Then set a count timer (like 60 seconds for example). Make this gloabl to the script so it's always available.
Then when someone hits the page, check the current IP address to see if it is in the DB. If it is, check the currrent date/time with the counter added against the date/time stored in the DB for that IP Address. If the user hits the page twice within a minute (as in our example here), then you don't add the hit. If it is outside of the minute time, then add the hit.
I don't have time to give code here, but I have given you enough to go on, that you should be able to build it... If not, go to HotScripts.com, and look for a counter script you can pull apart. That basic concept I explained above is the same principle in most counter scripts.
