Drupal user one off settings I am putting together a complex Drupal user driven website. One thing I need to accomplish early on is to put users into groups as they register.

Can anyone tell me how I can get them to register particular details which they will not be able to amend in the future? Such data as the users gender etc....?

Thanks.
For the user groups, use the auto assign role module and you could use content profile and CCK to create profile fields that the user can fill in.  You could use the content permissions module that's a part of CCK to allow a user to create a profile but not to edit certain fields once they've been created.