Error 7 (Windows error 14003)

I am trying to install iTunes on my sister's computer and keep getting the above code. I have uninstalled and reinstalled numerous times. What am I doing wrong? I should note that in error today, on MY computer, I reinstalled iTunes and used her e-mail address. She keeps insisting that is the reason I can't put it on her computer, because I used her e-mail address installing it on our computer. I know that has nothing to do with it. Please help me get this installed on her computer.....we are very tense around here.