Javascript Submit Problem : Form Won't Submit

So, here's my problem :

I've created a table in my document, presenting a list of items, one
can 'select' by clicking on it... (Kinda like a menu, you make your
choice from) But since this table can get very long, I've put
something of a 'search-form' on top, which enables the user to make a
selection of products from the list.

Now, the form uses a "post" method, and submits to itself, using the
form action. Some PHP script will make sure that the form is filled
out already, the next time it's presented.

The table, containing a list of products is presented, below the form.
When a user clicks on a product, the product should be "selected". At
first i just used a <a href="zoeken.php?prod_id=24"> link to do this,
but the problem is that my form won't remain in tact.

So now, the global idea is to submit the form after setting a hidden
form-field using JavaScript, using a onClick event.

Here's my code :