Is there a way, on installation of a new wiki, to
completely disable the
talk namespace? No talk pages, "not nowhere, not nohow," as the wizard
said.
In addition to Chad's hint you might have a look at
http://www.mediawiki.org/wiki/Extension:NamespacePermissions_Extension
But I think this extension will only work with custom namespaces, not the built-in ones.
hth
Frank