I'm currently working on a website that requieres quite a tricky menu structure. I've been trying to figure out a solution on my own for several weeks, but I still can't get near it. Maybe it is even so simple that I'm just thinking too complicated for it

So and now I'll try to describe my problem as detailed as possible.
The website I'm working on requieres a 3-level menu structure that looks something like the one on the pictures I attached to the posting
The first level (1.gif) is always present on the top of the website. It's just a simple horizontal text-menu without big special effects with the exeption of hover. On hover or after clicking on the 2nd menu element we get another simple hotizontal menu under the first one (2.gif). Till here it's not very tricky but the complicated part starts from here. As the user clicks on the menu elements 2.1 or 2.2 or 2.3 etc. a third simple horizontal menu has to appear under the first two ones, but in each case it has to display their own 3rd level menu elements (in that case children-elements) ONLY (3a.gif and 3b.gif). The Problem here is that while 2nd-level menu elements stay the same on every page, 3rd-level menu elements have to be different for every subpage.
I would be very grateful if someone could help me with this problem. I suppose that I'm not very good at describing problems so if you don't understand something I could try to explain it better and if you need some additional information (e.g. stylesheets or templates) I'll add it asap.
Many thanks in advance!
Greg