Focused on Revit Structure but I imagine just as relevant for the other versions, just a copy of what was posted at the BIM & BEAM blog: Here's the text of their post, be sure to check out the rest of the blog.
We had several users reporting crashes when they import or export dwg files with Revit Structure 2008 for the following build numbers:
DVD Build is: 20070324_1700
Web Build is: 20070404_1700
We did some investigation and we found out that the reason was related to the presence of an old version of DWG TrueView on the computer.
In order to so fix this issue, you need to uninstall DWG TrueView and upgrade it to the latest free version available at http://usa.autodesk.com/adsk/servlet/mform?siteID=123112&id=9078813 . After the upgrade of DWG TrueView, RST2008 should be able to import/export DWG files properly.