Node Hierarchy CCK Field

Hi there,

I have to create a content type with a "multi-dropbox" or "multi-autoselect" widget.

Here is the context : the node must be associated with a "client" (node reference). A "client" can be a "group" or a "site", "group" nodes being parents of "site" nodes thanks to node hiearchy.

Now I just allow the user to select a "site" with a node reference autocomplete or dropdown widget but the user has to select the site browsing all the groups in the widget.

What I want to do is to allow the user to first select the group then the site

The hierarchical_select (http://drupal.org/project/hierarchical_select) module is exactly what I'm looking for but it works only with taxonomy or menus. I would like something like that but with nodes.

Does anyone know something like this ?
THanks