Hi
At the moment sub-navigation is not "easily" supported however it is
possible. To achieve top level "nested" navigation you can use special
blocks, here is how:
1. Open up admin/themes/{current theme}/settings.php
2. Change $nested_nav = "no"; to $nested_nav = "yes";
3. You should now see a second level of navigation on any dynamic
page.
If you play around with this you should be able to create 2 levels of
navigation.
Other options include:
1. Replacing the auto-build navigation with your own un-ordered list.
2. Creating a module that supports different URLs and then using a
block for sub-navigation (same as
http://www.getpixie.co.uk/support/)
Hope that helps
Scott