Adding tool tip for profile links

I was trying to figure out how to get tool tip for the profile links on in my Elgg installation.

In smiple way, while hovering cursur to the username (user name with link to his profile in entire Elgg). To get a tool tip box, with his thumbnail (link to his profile) and Add friend link within the tool tip box.

I was looking on this link 

http://dojotoolkit.org/documentation/tutorials/1.6/dialogs_tooltips/

Can someone guide me from where to start. As per i understand, modification will be done in Profile plugin, But from where to start ?

Suggestions are welcome.

Thanks