How do I access a USB drive on my Airport Extreme?

I have a new Airport Extreme with a MyBook USB disk connected. I have file sharing turned on with a disk password. I believe everything starts up ok, but I do not see the disk listed anywhere that I can access it. I'm running in a Windows XP environment. I have all my iTunes on the external disk. I need to be able to name the location of my library. It should show up under My Computer as a network disk, I think? If not, how do I access it?