I have gotten around this issue in a wss site by utilizing a links
bar to simulate the tabs, and linking each button on the link bar to
a web part page. Working with the link bar needs to be done in
frontpage, but it is pretty easy to do.
Additionally, if you store the webpart pages in seperate document
libraries, the pages will inherrit the permissions of the library...
making it possible to permission a page to a specific group.