Best way to execute actions within a class

I have been building a lightweight PHP4 based, hopefully PHP5 OO structure where each page or php file contains its own class which is then executed using the constructor like so new SomeProject_SomeSubProject(); within the subclasses contructor I then call a method called start which is in a base class called Page which is extended from the main project class called SomeProject. Within start it calls a method to check action page get uri's ie ?action=view , what i used to within procedural code is use switch statements but seem taxing. Within this now will check if its a get or post method and execute a method in the class with the same name ie public function action_view() or if its a post method i have chosen to call it post_action_view(). Now is this a good setup I would like some feedback on how people in an OO world would achieve this. Now that i have started executing constructors within the main page files, I have come to think of better ways passing around a url possibly like something like this someurl/index/someproject_somesubproject/view or someurl/someproject_somesubproject/view or someurl/index/aliasofclass/view or someurl/aliasofclass/view and for adding keys to the end for db stuff something like someurl/index/aliasofclass/view?ID=1 or someurl/index/aliasofclass/view/ID/1 i think then all u need is the main index.php file which works out which class to load and execute ? And possibly peristist the objects loads too via shm maybe ? And if you need other files it could be like someurl/otherfile/aliasofclass/view/ID/1 I'm sure this is all mod_rewrite stuff, is this taxing to do ? Let me know always open to suggestions especially ways to do caching better.