why won't my computer allow me to install itunes?

ok, so i just got a dell latitude yesterday with a special configuration for the university of scranton which i will be attending in the fall...i was attempting to install itunes on the computer, which at first sight appears to already be installed but in reality when you click the shortcut it prompts a configuration process to begin which always ends in me being told that it cannot write some sort of key...when i try to access the download via the apple website, the download goes fine until i am told during the installation process that it cannot create a temporary folder necessary for the installation before erasing the entire install process

i really don't know a whole lot about computers, so some help here from someone with knowledge would be greatly appreciated