Get node content from jquery in block

I've created a module that has a block that uses drupal_add_js to the page. In this JS/jquery I'd like to dynamically change the content of the block based on actions on the page. For example, on a node/add form, if a user selects a node from a cck node reference dropdown, I'd like to change the content of my block to reflect the selected node - by pulling in the node's author, title, cck fields, etc.

Any thoughts on how to accomplish this? I've seen solutions using drupal_add_js to pass in variables, but that won't work since I need to dynamically determine what node I'm pulling different fields from.

Dillon