javascript ?

Hi !!! I know maybe this is not the right place to make this question but I have been a PHP user for long time and this list had been very helpful. I want to create a form which once you select a radio button or a drop down menu display the proper fields according to the selection. Let say that we have two options : To go and Pick Up. If the user select to go then automatically display the address field, zip field etc, if the user select pick up display the time field etc. I 've been looking a lot of javascript sites but can't find something similar to that I want. Hope any of you can help me. Thanks in advance. Angel.