Show nr of people viewing a page in the nav menu like in vbulletin

Hi,

vBulletin has this:
vBulletin Announcements (26 Viewing)

There you can see how many people are currently viewing the page.

I would like somthin like this in my nav menu like:
Pages
? About (1 viewing)
? Sub (0 viewing)

Of course with some AJAX to keep it up to date!
Would be cool to have this!!!

Null