Working with lightboxes and custom logins

I have what I believe should be a simple requirement for a user experience. Right now I have a sign up/login page that is largely the default, out of the box, functionality. However, after the user logs in or signs up they are dropped back to the main page. I want them to get re-directed to another page of my choosing. When I have started poking around it appears the only real page I can redirect them to is the “My Account” page which is not helpful. The page I want to redirect them to does have the username in the URL which I can imagine can be a problem. Anyway…My primary question is:

Is it possible to get users to redirect to a different page other than dropping back to the home page? If so how?