As in most things *nixish, there're several ways to do many things. Here's but one method:
To manually set interface IP addys:
IN the Gnome menu bar - click on System > Administration > Networking. Put in your root password.
Highlite the interface, click on Edit. Do the do.
IP - 192.168.1.2
gw - 192.168.1.2
IP - 192.168.1.3
gw - 192.168.1.3
You'll find a tool in the Administration > Server Settings > NFS menu to help configure your NFS shares. You can also use man exports to read up on how to manuall configure the /etc/exports file.
You can read up on NFS for how to configure your /etc/fstab file to automount these shares on bootup.
And yes - you'll need to setup the NFS shares one each machine - if you want to have access to that files machine from the other. If all you need is a common share point accessable by both machines, then no. Setup one of them as an NFS server and then access those files localy on that server, and via NFS from the other PC.