navigation customization

I've been trying to make this work all day, and I've read countless web tutorials, all of which have ultimately been dead ends. Hopefully somebody here can point me in the right direction.

So I'm working on a site that's divided into sections, subsections, and sub-subsections. A hierarchy something like this:

• Home
  • About
    • detail 1
    • detail 2
  • History
    • detail 3
    • detail 4
• Community
  • Staff Bios
    • staff 1
    • staff 2

I'd like to have the primary sections ("Home" and "Community" in the example) appear as tabs at the top of the site. Then, based on whichever tab you click on, you should be shown a vertical navigation bar that's got 2 levels of nested links, but only shows you the options within the section that you clicked on. So, when you first hit the page, you are at the home page and the navigation menu will have "About" and it's sub-items as well as "History" and it's sub items, but you don't see "staff bios" at all. Then, if you click on the "community" tab, the "about" and "history" links are gone, but you see the "Staff Bios" link & sub-links instead. My problem is that for the life of me I can't figure out how to get a nested menu that also is aware of what section the user is in. The closest i've been able to come is using the Primary and Secondary links features, but even if I set up tertiary links & turn on the expanded flag for all the links, the php call for the secondary links doesn't bring up any of the sub-items. So, I end up with "About" and "History" showing up perfectly, but "detail 1", "detail 2" etc. don't show at all.

Is is possible to achieve this effect using the primary/secondary link calls or is there some other approach that's better? It's ok if the links for the sections are hard-coded into the templates, since I won't need to add new sections once the site is set up. However, users of the site will need to add various extra sub and sub-sub menu items over time. I'd really like something that produces just a couple of nested unordered lists with links, rather than something like the admin menu where there's little triangles that you have to click on to expand: I need the whole two-level hierarchy to be visible at all times.

Finally, I need to use slightly different templates depending which section of the site the user is in. I've found a number of ways of implementing this, but I'll need the solution to my menu problem to be compatible with at least one of them.

The easiest thing would be if there's just some parameter than I can change somewhere so that the secondary php function returns the tertiary links as well, or some other function call that accomplishes the same end.

Thanks!