You can download the server version
here. Unzip it in a separate folder on your most powerful machine. Then start it up using the 'ServerStart.bat', and the first time it starts it will generate some extra files, like 'server.properties'.
If you want to play Minecraft on the same computer as the server is on, you have to have at least 8 gigs of memory and a 64bit system... but you probably found that out already. All you need to find out now is the IP-address of the computer, which you will need on the other computer to make the connection to the server.
Open a command prompt (Windows-R, type 'cmd'), and type 'IPCONFIG' on the computer where the server is running. You will see a line starting with 'ipv4 address', memorize the number behind it (or write it down).
On the other computer start FTB Direwolf, and go to multiplayer. Click 'add server', Put something meaningful in Server Name, and put the number you somehow still know in the 'Server Address'.
At this point you should be able to log in to the server, there should be vertical green bars after the server address.
Follow the same procedure for the other computer. If it's the same computer as that which runs the server, you can use 127.0.0.1 as the server address.
