I have Lynksys router and behind it two computers. I would like to allow my friend to access from internet to my computer and vice-versa. We would like to be able to share files and act like we are in the LAN. Is this possible to accomplish and how. I hope you will be able to tell us what to do and how to configure rooter.
Configuring router is just one part of the job (smaller). You will have to configure VPN (Virtual private network) whish acts like secure tunnel between two computers over internet and enables just what you want to accomplish. When you start VPN you have in router configuration, under security, possibility to tell router to let incoming VPN connections to your computer. This should do the trick.