Attached Link: http://www.poseworks.com/serendipity/index.php?/categories/4-PzrXml

> Quote - I assume(d) that something like this was bound to have already been written, so I didn't want to reinvent the wheel if it was already available.

I'm sure some of ockham's scripts have actor selection.
These will be tk list boxes (with multiselect turned on when appropriate) that are populated at runtime.

Quote - Can you even do tree-view gadgets using the PzrXML library?

Not tree views.
Poser's own dialog stuff is quite limited in scope, posework's library allows dynamic creation, so you can build a list of actors on the fly.
Tree widgets are available (and have been for a long while) for tkInter, but need to find and install them.
Tix has the sort of widgets your wanting (see -> http://tix.sourceforge.net/dist/current/docs/html/TixUser/subsubsection3_3_1_3.html#SECTION00031300000000000000), has Python support and build support for it is part of the Python distribution.
It's not, however part of Poser Python (no DLLs or tcl files), so you have to obtain and install.

Quote - And, where can I find info (docs, etc) on that library?

See attached link.