These are tutorials I have written for mapping in GTK radiant or in Worldcraft. If you have a tutorial you would like written then e-mail me and i'll see what I can do.
GTK Radiant Tutorials
None at the moment. Make a request.
(Note - I take no responsibility for any damage these files cause to your system (I have virus scanned them, and I have a virus guard, but you never know so I am writing this to be safe))