nuhi, all the files EXCEPT boot.wim and install.wim in sources folder. those files are for running setup.exe within windows (upgrade or custom install). just look at the #2 of boot.wim, it has all these files in sources dir in the wim ( which will be loaded to ram during DVD boot install or recovery) and files in the DVD\sources dir are not used in PE AFAIK the .clg files are catalog files for respective edition,used by the WAIK, dunno what it does. trust me, they are irrelevent in DVD boot scenario, till now i havnt come across with any problems from them.