There is absolutely no reason to login as root. The very fact that you are asking this question means that you are setting yourself up to hose your system by accident. It is a dangerous practice even for users who know what they are doing. Cleary, you don't. As for moving your mail to a new account, all you have to do is to find your Eudora files in /Macintosh HD/Users/{administrator account}. Locate the same folder in /Macintosh HD/Users/root/. Move files from {administrator account} to the corresponding location in root. However, I cannot be more emphatic--what you are trying to do is about as bad an idea as can be imagined. Don't do it.
