Hi Sylvain, Eric,
Thanks for your replies. The ._ files are the resource fork, as you pointed out, which is why "find" and other commands can't see them. The 10.4 "tar" command includes them automatically, and doesn't seem to provide a way to turn them off. :-( Fortunately, "rsync" does, so I solved my particular problem by doing an "rsync" of the project to /tmp and then tarred it up there.
Thanks again for the pointers.