This article was first written in June 2004 for the BeezNest technical website (http://glasnost.beeznest.org/articles/135).
To change the default printer when using GNOME, it is pretty easy, provided that you use CUPS and gnome-cups-manager.
Go into the “Applications” menu, then “Desktop Preferences”, and “System Tools” and click on “Printing”.
There, you have a list of all preconfigured printers on the system. Right-click on the one you want by default and click on the “Make Default” menu entry. If this one is greyed and you cannot click on it, it means it is already the default.
Now, any application should print on this printer by default, unless otherwise told.