[kh99]

You mean two clicks per hour on the clock, so for instance they click twice at 1:59 then twice at 2:01, but not again until 3:00? Then yeah, I think I'd make a table with ip, time of last click, count this hour, and total count columns. Updating is a little tricky since you could get two or more near-simultaneous clicks from the same ip, so a "read, check the value, write a new record" sequence could end up with unexpected results.

You probably know that more than one user could appear to come from the same ip, and one user can come from multiple ips, so it can be a problem trying to use an ip address to award the prize (like if two users clicked from the same ip, who wins?). Not to mention the fact that if they don't have to be logged in you have to do the matching of user to ip somehow.