intercepting URLs in a "control-system"

Please forgive any obvious ignorances on my part, I am just learning PHP... Having read quite a bit on-line, I am interested in trying to "trap" URLs sent to my site so I can process the request and respond without neccessarily having a "real" page to serve. If this makes any sense, how do I do it? Because I expect that apache (in my case) would not like a URL that contains extra directories/files and would reject it. An example: Web Site Root: www.abc.com/index.php On that page are "a" tags to further information but which physically don't exist. It will be automatically generated from a database. For example: www.abc.com/cars/volvo/X70.html If I don't have that directory tree and a file called X70.html. Could I "trap" the http/URL request (BEFORE apache throws it out) and process it in my PHP control-engine which will find the right information and respond accordingly? Thanks in advance, Alan PS, if there are any examples of this (GPL) which you know of, please just pass me the link.