Move the old Extensions.mkext to the trash -- is this the one in /System/Library/ ?

and rename the new file to Extensions.mkext. -- i'm a little bit confused here, do you mean the Extensions.mkext that copied to the desktop previously? if so, it doesn't need to be renamed. or by "the new file", you mean some other file?

drag this to the /System/Library/ Folder -- just to confirm, it's the "Extensions.mkext" file on desk top?

while in this folder, --what do you mean here?

sorry about my english... and thanks for helping