There are a couple of events that occur while your creating a new user with the CreateUserWizard
control (specifically the FinishButtonClick
and the CreatedUser
events). You could handle either one of those events and do your custom SQL insert into your aspnet_UserInfo table in the event handler.
This MSDN tutorial is a great resource for customizing the CreateUserWizard
process.
I don't know of a way to find out what specific SQL statements are executed when the library functions are called to create a new user. That doesn't mean there isn't a way though, I just don't know it =)
Addition (based on comments): Considering your use-case, look in the code-behind for your "Register.aspx" file. There is a line in there (by default) that looks like this:
FormsAuthentication.SetAuthCookie(RegisterUser.UserName, False)
Just delete that line and you'll be good - your Admin will continue to be logged in as himself after creating the new user.