I also had hugh problems with this one.
The best thing to do is use the search function on this forum, using words combo box add records - I used this and now if user enters a name not in combo box, i get a message box prompt - whether to add new user or not, if yes will open add user form.
As for linking combo box to query/table. Delete combo box (if havent already) then add making sure the wizard is selected on the toolbox. The wizard will guide you through the rest of the process and you can specify to select records from a table or query.
Hope this helps and good luck.