We finally found a workaround to the hangup-crash issue when Exporting in Revit 6.1, to ACAD 2004 DWG/DXF, with very large files.

Our Revit Library, Templates, Families, and AccuRender are located on a network share, which turns out to be causing the hangups.

Solution:
Copy the revit file to the local computer if it's saved on a network share. If you have linked files those should be copied locally too.

Disconnect the computer from the Revit share, start Revit (which produces errors that it cannot find it's templates, etc), load the revit file, Then export dwg/dxf to the local harddrive.

This workaround has been 100% so far for us!

LB