ubun2

i am new to the linux world and in my endeavor to learn more i have been experementing with shell scripting.  i am following a tutorial at linuxcommand.org in which the author takes you through the process of writing a script that produces a HTML page with your system info.  at the part im at now the script makes use of the "du" command. using this command means that in order to run the script you have to be the root user.  i can do it but whenever i run the script as root i have to specify the full path in order to get it to work.  this is tru also for a much more simple script i wrote with only one command.  how do i make is so that i can run the script as root.  i have already added the directory in question to my "path"  any help would be appreciated.