problem opening microsoft courseware fil

Im a trainer in Stockholm preparing new courseware for Windows NT 4.0 administration. Before he went on vacation an MCT colleague sent me two ZIP files, each containing a Microsoft offic?al courseware powerpoint file to be inspired by. Problem is it won’ open. The zip seem undamaged, but it will give me an error when I try to unzip it, stating that the checksum is wrong. I tried to PKfix the files but that dont work either. The files where sent on two different occations, so I dont think that the zip fils would both be corrupt. Is there a special trick opening these files??

/Mats