I want to customize the user/register form.
When the anonymous user goes on this page I don't want to show the tabs Create new account, Log in, Request new password, and don't want to see the fieldset Account information with a username and email.
How can I do it in Drupal 6?
The tabtamer module lets you control what tabs are visible from the admin pages.
I'm not sure if it's possible to remove the user profile page entirely, but a module like login_destination or logintoboggan let you control where the user goes when they log in.