How do I auto-populate data regarding a USER from the submission values of another form.

I have a site registration form and an event registration form.

The site registration form saves the submissions such as First Name, Last Name, emailID and a number of other information in it's submissions table. Some of the information such as the UserID, emailID are also saved in to the Joomla! User table as the site registration.

The event form is for registering for an event. When a user login to site using the credentials from their "site registration" form, I would like to auto-populate their first name, last name and some of the other information to the event form.

How do I access the data from the site registration submission and display it on the event registration? I think it is just a matter of accessing the appropriate table and pulling the data related to that User. But I am not exactly sure where the submissions data is stored from each form and how to read that informaiton.

Any help would be appreciated.

Thank you,