I would like to know how I can update the database table, from my own form in WordPress. I can do this using regular PHP MySQL, but when I go to use the $wpdb class, I have some problems with it. Can someone let me know how to do this. What I want to do is very simple, just take a form like the following:

Name:
Last Name:
Address:
Telephone:
Email:
Subject:

and then move the entered values into the database, using the $wpdb class.

Thank you very much,

Ricardo