I am setting up a new nix box and would like to have the following configuration.

IP address: 192.168.0.5
Netmask: 255.255.255.0
Server name: mailserver.abc.co.za
Gateway : 192.168.0.1

I need to know which files i should edit to achieve this, I know there are 4 files to edit but have forgotten the names of them that a friend gave to me.

This would be distribution specific, as each distro does things a little differently and often use their own programs for configuration network connectivity. For example, under Slackware you would configure the IPs under /etc/rc.d/rc.inet1 or set it up with "netconfig", but under a different distribution it would be a completely different situation.

The only thing you can really be sure of is that the DNS servers will be configured in /etc/resolv.conf and hostname will be in /etc/hostname. Beyond that, the only way to get it working in any distribution is to place the commands themselves in the rc.local (or similar) boot script, like: