You do not need to install an all-Microsoft environment for your small office, if you do not need very specific applications. Linux can answer all your network administration needs, from a couple of users to large local area networks (LANs) to wide area networks (WANs).
Introduction
Typically, for your small office you need to have office applications, a network server, a groupware application, proxy server, file server and an anti-virus server. You do not need to go for expensive Microsoft Office and Exchange applications for these purposes. You will benefit from huge savings using Linux and have your cash to spend for more useful things, such as further investments in your business.
Office Applications
We have done an extensive review of Linux office applications here in Brighthub. For KOffice you can go here and here, for OpenOffice.org here, for GnomeOffice here and IBM Lotus Symphony here. However, before selecting which Office suite to go, I advise you to check Microsoft Office compatibility extensively before full deployment. In this perspective, OpenOffice.org stands as a stronger alternative. For the office programs that have e-mail and personal information management, it will also be wise to check its compatibility with your groupware server (see below.)
Groupware
There are many applications available as groupware applications. You can have a look at Open X-change, Kolab and Citadel. I will not go into the details for analyzing them one by one (out of the scope of this article) but for your small business, I strongly recommend you to go each one in detail, get into contact with the developers and find the one that meets your requirements. This is a very important step because once you choose one it will be very costly if not very difficult to go back and start with a new one.
E-mail
If you do not prefer using groupware applications but prefer a stand-alone e-mail application, then you can go for Postfix. Do not be fooled by the cute website and assume that the application is too casual for business use; you can not imagine how many businesses use Postfix as their e-mail transfer program. Anyway, if you want further choices you can look at Squirrel Mail, Courier or Cyrus. And you also have the option to enable webmail for your employees. Linux is full of choices, remember?
Antivirus, Antispyware and Antispam
No matter everyone tells Linux is free from viruses, trojans or other malware, you have to build your business’s system with security in mind. For that matter (and to keep your sanity afterwards) I strongly recommend you to install antivirus, antispyware and antispam on your server. There are powerful tools for these purposes: Amavis-d for spam and virus checking, SpamAssasin to filter spam and ClamAV for virus scan.