Yeah, you need a webpart which has the IParametersOutProvider connection interface implemented, and I don't think any of the ootb MOSS webparts have that.
I'd say you have two options here, which involve development:
1. Create your own doclib webpart, with the correct connection interface - and connect it directly to the RtGraphic webpart to provide an SVG path
2. Create a hidden "man-in-the-middle" webpart, which takes parameters from the doclib webpart, and sends them to the RtGraphic webpart.
(Tutorial on creating your own connectable webparts: http://vcampus.osisoft.com/bloggers_place/b/cristobal/archive/2009/12/04/how-to-create-custom-webparts-that-connects-with-osisosft-s-rtwebparts.aspx)
A third option, which doesn't require development, would be to set up the RtTreeView webpart to show the structure of all your graphics. This is the quickest way to set up a menu structure where you select graphics and see the results in a nearby RtGraphic webpart. The downside here would be the need to manually maintain the menu structure (in AF or MDB)