How can i hook to the user registration and login event?

I want to execute some custom code after a user has registered or logged in.

Tnx

Thanks for your answer.

Of all posibilities this is the one i did not think of..

Admin Menu -> User Accounts -> "User Settings" (at bottom of window) -> "Redirect after Login" and "Redirect after Registration"

I created a new module that executed the code I wanted, installed it on a 'dummy' page and now have the "Redirect after Login" pointing to that 'dummy' page.

Hope this helps!

CJ