If you want phpBB within a Tiki environment, then try http://www.tikipro.org. phpBB is GPL licensed which is incompatible with the TikiWiki LGPL license. So our own forums will be around for awhile, probably in need of a re-write, just like the search.
1.9 did address limiting search results to onlythings you have permission to access, but this should be properly tested before you use in a live situation where eyes shouldnt read certain things. Personally I wouldnt trust it just yet. (Oh and its mysql specific )