Dep error for itunes

Help! I have been trying for 4 hours to disable the Data Execution Prevention in order to be able to download the i tunes program for my i pod. I am not computer savvy but I CAN follow instructions. The problem is that I have a desktop with Vista program and cant figure out the DEP code to allow for i Tunes to start running. The Popup that comes up is iTunes has stopped working. I have more than 20Gigs of music on my iTunes and now cannot access it. Please Help Me