mn-500 sharing problems

i'm using winxp pro, and in my workgroup i have two
computers listed. i only can share files in the shared
documents section. i only can access files from my main
computer to and from my 2nd computer shared documents
section. i can't access any files at all from my 2nd
computer to the main one. it says you need permission to
access the main computer. all my sharing folders are
enabled on both computers. how do you allow complete free
access to all files on both computers?