Hello Jack
PIX/ASA 7.2 do not support a high range of URL control ! In any case, it does support blocking of certain URL's using the Modular QOS configurations.. You can refer to this URL to accomplish this:
http://www.cisco.com/en/US/products/ps6120/products_configuration_example09186a0080940c5a.shtml
This can be a starter for you, but i would highly recommend you to buy a third party URL filtering software like websense.. This can not only block URLs, but give you a lot of good reports, on top users accessing http, people who have visited blocked sites etc, with EASE in configuration.. With Normal ASA CLI, it might take a nightmare to block a single URL !! with websense its just a touch n go !!!
Infact with ASA u have the CSC module which can do most of the things that websense does... but unfortunately u dont have a ASA, only a PIX, and hence this option is not valid !
Hope this helps.. all the best. rate replies if found useful..
Raj