Need help with functions

I'm into developing a shopping cart using PHP (naturally) and am running into a little snag. I need to be able to perform several tasks within the framework of a <form></form> construct:

1)      Call a function from within the module;
2)      Call an external PHP module (no return) with the contents of ALL elements within the form;
3)      Call an external (or a function) that will overlay a smaller window to display cart contents and
        have the customer click a button to close the window (return?). All FORM contents needed;

Here is the pseudo code, subject to MAJOR change (obviously) ... <? function function_one() { print ("I'm in function one ..."); } ?> <html> <head> </head> <body> <form> This is program one ... <? print ("<a href=\"bob2.php\"> click here</a>"); <---- This needs to transfer to

                                                          another module, not returning.
  print ("<input type=???">);                       <---- This needs to enter function_one
                                                          and remain within the module
  print ("???????????????");                        <---- This needs to transfer to another
                                                          module (or call another function
                                                          within this module) to open another
                                                          window, display the contents of a
                                                          shopping cart, then have the customer
                                                          click a button to close with window.

?> </form> </body> </html> Can anyone return this with some pseudo code? Bob