[Typo3] put different level of menus on different page?

[Bing Du]

I'm able to put different levels of menus on different places on the 
same page.  But how to do that on different pages?  Here is the page 
structure.

page1
   subpage11
   subpage12
   subpage13
page2
   subpage21
   subpage22

What I want is the top level page only shows the following as left hand 
side menu.

page1
page2

When clicking page1, the page will refresh and show page1's subpages on 
the left as menu:

subpage11
subpage12
subpage13

Clicking page2 does the same thing, but this time shows page2's subpages 
on the left as menu.

I've tried doNotShowLink without any success.  Should I use template 
extension?

I'd appriciate any hints or pointers.

Bing