Fairly simple.. you'll need to setup and install samba server for file sharing abilities.
Everything you need relative to samba is hereits a pretty straight forward read giving you step by step how to information.. You'll need to do this to both the systems.
then go to your network place? or just type smb://nameofcomputer in a nautilus window and you'll be promted for a password. enter the name and password you created on the box your trying to access and you'll be in.