I seem to have had success in recovering my stuff off the 500 Gbyte drive. All my jpg's mp3's avi's vob's etc are alll there and working.
If I understand you correctly, any file structure that is not recognised is recovered as a zip file. If this is so, any "zip" file which will not open should be one of the non specific files. In this case I assume I should change the extension to .odt or .ods for open office writer or spread sheet type files and see if they open.
Cheers
Pete
Update: I changed an open office file extension to .zip. Double clicked the file which allowed me to see its structure. I then double clicked the recovered zip files of about the right size. The ones which had the right structure were edited to .ods extensions and have now all been successfully recovered.