prototype onsubmit not working

[eluser]winterain[/eluser]
well well.. I think my brain started working again...
I've come to the conclusion that the cause of my initial problems were:

1: I was using an onchange submit() instead of pressing a submit button directly to trigger the JS.
Question now is, how can I change the onsubmit to work with onchange=this.form.submit(); ?

2: the $F('categories') aka getValue() function is not working correctly by getting the list menu item, as it is not an input field. Again, any ideas how to correct it?