I have a solution for the relative path problem in PowerPoint 2010. It is different than what was posted, but close.
1. Open PowerPoint using the start menu, or a shortcut on your desktop ONLY. Do not double-click on the Whatever.pptx file.
2. When PowerPoint is opened, go to the Open menu and select the file through the normal file selection process. Do not use the Recently Opened selection, as this doesn’t work correctly for the Speechover files.
3. Once the file is open, go to the Speechover tab and select Preferences. Make sure that the box is checked for “Use relative paths for sound files”. If this was not previously checked, when you click on Save and Exit, it will ask if you want to refresh all slides. Click Okay.
4. Form here on, when you want to make any changes to the Speechover files, you MUST open PowerPoint, then open the file using the Open File menu. Otherwise it hoses that Speechover file.
It appears that if you want to just edit the PowerPoint content without editing the Speechover files at all, you can double-click on the .PPTX file from Windows Explorer and not affect the Speechover relative paths.