Consideration on Upgrade php

Dear all Currently i'm using PHP 4.04 in my Web Server, i heard that there is a bit different on the newer version of php! Like : something different in php.ini! I know that the newest version of php is 4.2.2, could someone pls tell me if there is different between PHP 4.0.4 with 4.2.2? I heard that when you post data from a form to other page, 4.2.2 will have problem, unless you got to set something from php.ini? is that right? -- Thx a lot! Jack nedcor4@nedcor.com.hk