How to allow a block on a page to load another block on same page in Drupal 7?
As i understood from your problem, i think you can benefit from this lesson
Ajax node reader in drupal
http://www.youtube.com/watch?v=zyLmQtiSXgI

and there is a module called Ajax Blocks, can benefit u if u wnt to creat ur own module.

and as alternative solutions u can use
 http://drupal.org/project/colorbox_node
so the user profile loads in colorbox modal dialog