I have a kext file from the macbookpro forums that will let me use 4 finger gestures on my early 2008 macbook pro. I can't replace the current AppleUSBMultitouch.kext no matter what I try to unlock the folder/repair permissions etc and I know I'm in the administrator account. So I need to know the basics of modifying these (and don't worry, I have it backed up etc)