There has also been several mentions of free DWG converters. You can search for them on the forum, or here is one post about it from Djordje:
http://archicad-talk.graphisoft.com/viewtopic.php?p=108924&highlight=dwg+free+converter#108924
If you don't have access to the person who sent you the AutoCAD 2009 file, then you can use that DWG converter to create a earlier version file.
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