We want to run fedora core 12 is it possible to run it as a serverr and client on our office

Welcome to LQ

Any general distribution can act both a server and a client, provided relevant software is installed.

Meanwhile, could you be more specific about server and client's functions? What do you want to do exactly, in other words what are you going to use it for?

It is very possible.

Keep in mind that each version of Fedora is only supported for thirteen months. After that there will be no updates of any kind. At that point it is officially suggested that you do a fresh install to a current version. This is why a lot of Fedora users switch to Centos. Centos is RHEL(Red Hat Enterprise Linux) with the logos removed(built from RHEL source code). It is free to install/update (unlike RHEL) and is binary compatible with RHEL. RHEL/Centos 5 (5.4 current) will have support until at least 2014(no fresh installs until then). Fedora is essentially the development branch of RHEL, RHEL5 was based on FC6(RHEL4 on FC3).