Ex. Libraries: D:\ProgramData\Autodesk\RME 2008 vs. Program executable: D:\Program Files\Revit MEP 2008\Program
Now I know the "P" is lacking content but the naming needs to at least be consistent for library development sake... Using a staight OOTB installation on Windows Vista on the D: (not c:).
BTW, Kyle outlined this pretty well in the following location but for those who did not read it, the naming of some content and folder structure has changed in this build.