Inserting form data in multiple tables

Hi, I am totally new to Dolphin, and I am carrying out some extension of features for client. I want to insert the form data of a particular field in multiple tables. This form is related to a particular module, if it helps. How do I do that?

I also had another problem. The sys_categories table in my client's database has the value of the id field as '0' for all records. Is this something because of the client or it is standard in all Dolphin installations? If the latter, what's the reason for this?

I am going to edit the core files for this project. Will just add an extra parameter with default set to false, and will carry out the necessary queries in the insert function or somewhere. Thanks.