Had a similar problem.

odfconverter and odfconverter_integrator did a great job but missed one slide with XML charts on it.

Powerpoint Viewer 2007 just refused "cannot open file".

Read the follwing;
http://omnicode.blogspot.com/2008/03...open-file.html

Installed Powerpoint Viewer 2003 and the 2007 Office Compatibility pack. They work but they don't convert (anywhere I can see) to a file you can use. I could print to PDF using PDFCreator. Looks like the pressure is on to pay the upgrade tax.