User/Password Integration

Hello,

I really need some help.

I'm building an web application, and I have elgg as one of the services of my site.

What I need to do:

1) When the user clicks on "Register" it opens MyApp's registration form, instead of Elgg's registration form.

2) When the user do the registration, MyApp's will insert this user both in MyApp's database and Elgg's database.

Is this possible?

Thank you!