I assume that by "computer server for the Ethernet network and register with goverment office" you are refereing to setting up a pc on the www. There are other ways that you can do it.
What I have done in the past is set up a small local network that consisted of One PLC, Two PC's and a RAS "box". connected to to two modems. The PLC was GE both PC's were running Intellution iFix and everyone "talked on Ethernet. The PC's , PLC and RAS all had hard-coded TCP/IP address's that were given to me by the company IT dept. lets say 10.0.0.1 for the PLC 10.0.0.10 and 11 for the PC's and the RAS was allocated a range 10.0.0.20 thru to 10.0.0.25. Now in the above scenario there is no connection to the internet so there is no need to register any address's with Governement or anyone else. The PC's talk to the PLC just like "normal" and if anyone wants to access the system remotely (to program/monitor PLC or to log on from a remote source and connect to the scada system they simply use "dial-up networking to first create a connection to this site and once connected they satrt either the programming software or the scada software on their PC.
Now since the wide spread take up of ADSL. It "should" be relatively simple to get an ADSL connection at the Plant (preferably one with a fixed IP address) and then then you should be able to connect to this IP address say from your home ADSL "pointing" by your PC to the plant's ip address. Of course there will be certain considerations that need to be taken into account ( firewalls etc. ) and I am sure that there are plenty of people on this forum that can point you inthe right direction.
Apart form iFix I have done a lot of work with Citect in setting up ethernet networks. If you have any questions please feel free to either post them here or PM if you want.