Security Breach

It all depends.

Strong passwords
policies and permissions
dmz
vpn with encryption
locked closets with switches, routers, servers
certificates
the list goes on...

one thing you should always remember to do is to rename the administrator account, and create a user named "administrator", and then disable it.

PS - shouldn't you hire an mcse?

There are hundreds if not thousands of articles and books which have been written on the subject of network security. It is not an undertaking for the timid. You should research the subject on the net or pick up some books on the subject and/or take some security-related courses. Here are a few places to start:

http://secinf.net/
http://netsecurity.about.com/
http://www.interhack.net/pubs/network-security/

There are many, many more.

Cheers.

RW

You cannot prevent a security breach anymore than you can prevent a robber mugging you on the sidewalk.

You can take steps to lessen the chances from happening and plan on how to handle the incident.

The first step would be to hire a security professional to investigate your environment. For example, can I walk into your facility claiming to be a maintenance rep and gain access to a server and remove it from a building. This has happened in the past...