Generally speaking, TiddlyWiki is not geared towards multi-user
collaboration. That's mainly because user management generally requires
some sort of server-side mediation (e.g. resolving conflicts arising
from simultaneous editing) - TiddlyWiki's code is executed on the client
side (i.e. in the user's browser) though.
Take a look at this (still incomplete) article on the community wiki:
http://tinyurl.com/26zhvg
(http://www.tiddlywiki.org/wiki/Can_I_use_TiddlyWiki_as_a_multi-user/collaborative/server_based_wiki%3F)
Eric's idea for using separate a TW document would work though, provided
that you don't need elaborate access control with permissions for a
large number of different user groups.
-- F.
An enhanced server-side solution is in the works (I believe there will
also be access control - not sure to what extent though). No ETA yet.
-- F.