DOCBOOK-APPS: Linux file layout

I'm doing a little work with xfree-86, helping out with the move
to docbook.

One question that has come up is a default layout for sgml 'stuff'.

Request please, Linux users, whats a 'fairly' standard
a) location for docbook dtd's, stylesheets
b) layout within that location.

I know its going to be different for established users,
but for a newbie knowing docbook from nothing,
suggestions please.

Regards DaveP