For .rhosts to work, you must have user equivalency on both boxes... for that to happen, you must have the same user ID on both systems.

the .rhosts must be in the ~home for that user on both boxes and have the name of the other host/user in it.

#<hostname> <username>


As a security measure, it is good to disable this when not needed, especially if you use .rhosts as root across several boxes... As you may know, if you have .rhosts to many boxes, compromising root on one box would give root equivalency on every box listed in its .rhosts file. And that would be very bad...