IF you use Patition magic you don't have to defrag before, you just have to tell how much you want to leave for windows and how much you're giving linux, then the computer will reboot and do all the work in "DOS" mode, PM creates a batch file you could make one on your own but it's much simpler to use PM just enter a few numbers and call it a day, when the computer reboots again it will tell you if the operation is good or bad , if good proceed to install Linux, if bad try again to partition