Squid ACL blocking url's

Hi, I have managed to get Squid up and running on our school network this week and I'm keen to make use of the facility to block keywords in the URL. Not being familiar with regex I am hoping that someone in this list can help with a simple (if possible!) explanation. I would like to add that having been a Microsoft prisoner I am enjoying the new found freedom that Linux has provided, suddenly new ideas can be tried, excellent open license software is available (money is always tight) and I am hoping to get a few 386/486 stations up as X terminals using LSTP. Exciting times but it take a bit of time to get the Microsoft schema replaced with Linux schema!!. Regards, Andy.