Say you have created custom fields in DVDpedia and want the program to automatically fill them in: You can use the IMDB plugin a bit of programming. We are always looking to improve the application and are working on this as a feature right now, in the meantime you can create your own version of the IMDb plug-in and customize it. Take a look at this post (http://www.bruji.com/forum/viewtopic.php?p=11033#p11033) for information how to do that if you have a little programming knowledge. Otherwise this post also has a linked to a modfied version of the plug-in that will put composer into custom1 and cinematographer into custom2.
With the regular IMDb plug-in all the information can be downloaded but it goes into the credits tab as there are no set fields for those. Take a look at the IMDb Options under the plug-in menu, the last menu with a picture of a plug-in to set those download options.