Oh, I think you simply need to take ownership of the files on the other hard drive.

You need to be logged in as an administrator, and have "simple file sharing" turned off (note that you can't turn this off in XP Home, should you be using that). You turn off "simple file sharing" in "folder properties".

The ownership properties should be located at "Sharing and Security" -> "Security" and then "Advanced". There should be an "Owner" tab in the new window. Once you're the owner of an object, you can change permissions of the object and make it accessable for whoever.