A server of... what? What kind of website are you talking about?
In general, using PHP to stop clicking/re-clicking in short periods of time is possible only with a database that logs IP addresses. Not a very efficient solution.
What you're looking for is some JavaScript that you can use to replace all of your links... whenever a user clicks on your new links, a script would check to see how long ago they last clicked on a link. If it's less than, say, 4 seconds, they would not be allowed to proceed. Try posting in a JavaScript forum for a solution.
For your stats bar, you would need to do a simple loop:
<?php
/* Let's say we've found out the user's exp, and it is 2817 */
$exp = 2817;
/* Now we put each level into an array */
$levels = array(1400, 4000, 8000, 12000, 18000, 24000, 29000, 35000, 40000, 49000, 58000, 69000, 75000, 82000, 89000, 98000, 106000, 200000);
/* We don't know the user's level, so let's assume it's 0 for now */
$user_level = 0;
/* This will iterate through the levels we put in the array above.
If the user has more experience than the specified requirement,
keep iterating.
If the user has less, end the loop and set their level to the level
of the last number we checked. */
foreach($levels as $num => $exp_needed)
{
if($exp < $exp_needed)
{
$user_level = $num - 1;
break;
}
}
/* Now you can just use the $user_level however you want */
echo 'Ranking: <img src="rank_' . $user_level . '.gif" />';
?>