Horizontal main menu with vertical submenu !!!

Hi all,

got lost in forums and info.... Google hasn't been much of use too. Here is the issue :

I want to have horizontal main links (in line - probably in 'user3' module)
with
vertical sublinks (under, probably in module 'left').

The example bellow could help:

I ================================
--------------------- L1-link1 | L2-link2 | L3-link3 | L4-link4 | L5-link5
L1-sublink1
L1-sublink2
L1-sublink3
...

II=================================
--------------------- L1-link1 | L2-link2 | L3-link3 | L4-link4 | L5-link5
L2-sublink1
L2-sublink2
L2-sublink3
...
... and so on ...

Looks like the big deal is too split the main level links from the sublevel links and to let the sublevel links to show in another module. I just can not figure out where should I look for this settings. The "extended menu" seems to be the right one, but since I am much too fresh into JOOMLA works, from all the documentation i get not much.

I would appreciate and hints, tips and detailed info!

Filip!