As of Jan. 31, 2013, you will not be able to export Google Doc files to the older MS Office 97-2003 formats (.doc, .ppt, .xls), and will instead be able to export to the newer MS Office formats (.docx, .xlsx, .pptx).
If you use an older version of Office, Google recommends installing the free compatibility plugin from Microsoft, which will open the modern Office file types. More information
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