system wide gnome desktop configuration

[H.S.]

Hello,

How can I make system wide configuration changes in Gnome? For example, 
on all users' desktop:

1. Volumes icons should not appear.
2. CDROM and DVD icons should appear.
3. A bunch of PDF files (located in /usr/local/share/doc) should appear 
as links (these are some custom help files and should be easy to find by 
all users without having to know what "/usr/local/share" is!).

Suggestions?
->HS