Itunes reading from an external hard drive

Hi All I’m very new to this so please excuse me if I ask daft questions.

What I am trying to achieve is - Itunes on my ATV reading my music from my external hard drive (without the need for a pc to be running)

I have installed ATVflash and have downloaded all the installers suggested, nitro tv can see my hard drive and mp3 files.

I only have access to a windows pc using xp.

Can anyone explain the steps I need to take to get itunes to use my hard drive as its source libary?