What router do you currently have?!? Unless you have a high end router: cisco, juniper networks, brocade, etc. NAT should be enabled & running by default. NAT, or Network Address Translation; simply put - "is the process of modifying IP address information in IP packet headers while in transit across a traffic routing device" [see link here:
http://en.wikipedia.org/wiki/Network_address_translation ] As long as you have a router in place, NAT occurs automatically.
If you and your brother are on the same network, connected to the same router, there is no reason you shouldn't be able to play SC1 - I have LAN parties where we play with 4-8 of us, all behind the same router.
Now, if you are looking to play SC1 and you and your bother are NOT connected to the same router, or are NOT in the same physical location geographically... My friends and I play "over the internet, WAN games" via a virtual VPN program called hamachi [see link:
https://secure.logmein.com/products/hamachi/download.aspx ] This allows friends of mine in multiple states, or continents to play as if we were on the same physical network. Depending on your router, you might have to forward a couple of ports to your PC on your local LAN. [see link: hamachi ports:
http://help.logmein.com/SelfServiceKnowledgeRenderer?type=FAQ&id=kA030000000DGD6CAO how to port forward:
http://portforward.com/ ]
I hope this helps, take care!
