Revit is not backward compatible, so you will not be able to open 2009 files in 2008. As for your inability to open or upgrade 2008 files in 2009, it is hard to say. Are you trying to drag and drop the 2008 files on the 2009 desktop icon or drag the 2008 project file in the open 2009 application window?
If so, try opening the file through 2009 with the Open from the file menu instead. If your 2008 files still cannot be opened contact Revit support through your subscription.
Mel Persin, AIA
AEC Technology Consultant
Technology to Visualize and Realize Solutions
Modeling for the Future/Drafting in the Present/Building on the Past