This site helped me out with this, basically yoou got it. Setting up limewire (gnutella) was a snap.
Instructions
These ICS port mappings have been generously contributed by Practically Networked visitors.
All you need to do to use them is:
click on a link to download the map file
open ICS Configuration
Import the mapping (you can do this by double clicking on the map file if you have V1.2 or greater)
Use ICS Configuration to change the mapping Target to the IP address of the computer that you want to map.
Reboot your system.
NOTE! These mappings can be imported only by ICS Configuration V1.2 or higher.