This doesn't help immediately but at least gives us hope. I emailed Autodesk (August 2009) about the lack of downloadable content for Impression on the new exchange website and here is their response:
---------- Forwarded message ----------
From: Lisa Crounse
Date: Wed, Aug 19, 2009 at 3:58 PM
Subject: RE: Impression
To: <@gmail.com>, Travis Jones <@autodesk.com>
Hi –
Thanks for contacting me. There are plans to add content exchange in the AutoCAD Exchange in the future. In the meantime, I and working to have the old content posted to a place where users can conveniently grab it. I will post a notification in the Impression Communication Center when that content is ready for download.
Lisa