Modify Web Form

I need someone to update an existing web form. The web form already functions and inserts data into and updates two mysql database tables. I need 3 things done and are as follows: 1. Based on an HTML email link, I need a script that will insert a number into an order ID field on the form, for example [login to view URL] would open the form and insert the number 3521 into the order ID field. 2. When the user clicks submit, the data is then placed into an existing table in a record that corresponds with the order id number from above, however, if the record does not exist a new record needs to be added to the table. 3. One of the items on the form is list box, and I would like to get it to pre populate based on data if any in its corresponding mysql table field. I have all the other fields doing this, but I can’t come up with the right code for the list box. I will need this done within 5 days. Thank you for your interest