Linux DVD Authoring GUIs
There are a couple of GUI options for authoring DVDs on Linux:
tovid - more information available at http://tovid.berlios.de
'Q' DVD-Author - more information available at http://qdvdauthor.sourceforge.net/
Both of these tools are in the very early stages of development, however, they both show you what command line entries they are using so they act as a pair of stabilisers until you're ready to ride the bike on your own.