After you process the login, check the user name, determine the page they need to go to and redirect them.
Normally you would use the "FormsAuthentication.RedirectFromLoginPage()" method to create the auth ticket and then redirect to the page they originally requested or to the default page.
Instead, use the "FormsAuthentication.SetAuthCookie()" method to create the auth ticket without the automatic redirect. Then do a regular "Response.Redirect()" to the user specific page.
-Peter
peterlanoie.blog