Finding a particular parent - nav question

Permalink
Hi Guys

I have the following sitemap:
HOME
   -English
       -About
         - Subpage of about


I'm working on a bilingual site and I want to inlcude the menu based on where the user is (there's no menu on homepage). At first I just grabbed out the url, exploded it and checked for the presence of 'Enlish' and if it was present it would include the english nav. Easy enough.

However my lovely theory broke down when i realied the backend doesn't use pretty urls.

Being that I know the ID of the English page how can I check to see if the sub pages are children of that ID? This needs to work on all sub pages. Any one help?

Or in simpler terms. How can i get the sitemap based on a particular id?

Any idea how this can be acheived?