CPU usage going through the roof?

I’ve been away from the whole developer enviroment for a while, but it feels good to be back at Kirupa:}

Alright, a while ack a client had me make him a web traffic site. Fairly simple, a user logs into a surf and views sites every 20 seconds. With each new site, you get .8 of a credit. Credits can be used to put your site into the surf, giving your website traffic.

I have a top frame that has a js countdown, when $i==0 the lower frame(url.php) reloads.

url.php chooses a random site out of the database to be put in the surf.

this means that if 50 people are surfing, thats 150 times a minute that url.php is being executed, 9000 times an hour.

The client has gone through a few hosts because he keeps exceeding his CPU usage. All the hosts have said there are too many instances of php-cgi.exe.

My question is… is that too much of a load on a server? I’ve checked the code hundreds of times, its all clean. I’m only a php coder, but from what I know, this problem is caused because there are just too many codes being executed. If that’s so, how do other traffic sites do it?