Using game version 1.0 - 1.05 (the latest non-beta version):
You will need to learn how to forward ports through any NAT-ing network device (routers, cable/dsl modems functioning as routers, etc.)
Please visit this sticky and find the link to my guide "Networking and SINS" (right at the bottom of the original post). Check the date on the file to make sure it's the correct guide (Feb 14th/08)
In that guide I take you through the steps required to host SINS version 1.0 - 1.05
Using game version 1.1 BETA:
Version 1.1 BETA allows hosting without having to configure one's NAT devices (routers). This is possible because the devs have been working hard on new "tunneling" netcode called ALLOY. Please be advised this version is still in BETA and as such there will be less people using it (less players).
You'll need to visit www.impulsedriven.com and download IMPULSE (Stardock's new digital distribution system), install it run it, click the BLUE ORB (upper left) select "show pre-release versions" and then update SINS to version 1.1 BETA.
of course if you have further issues........feel free to ask!
thanks,
the Monk