You are setting up a server in a "Small Medium Business" (< 100 employees), which may be very simple or very difficult, depending of what you will want to do with it.
- substitute a windows server by a linux server is not as easy as it seems, but possible (just it might be overwhelming for the amateur/enthusiast, leave that for the matured professional administrator)
- add a linux server to an existing working network, is very easy and a good way to start with linux without any drawback, nor compromising the existing services. Benefit: linux services don't have licenses - they come free and forever :)
Window server does more than file sharing.
So to substitute it by linux, you will have to:
- understand all that windows was doing
- how to configure linux to do all that
- and migrate the configuration settings from the windows -> linux
And do it all in the backstage without the clients (employees) noticing any change (or they will complaint: if they are your friends they will laugh and joke the first day, but not after 5 days of suffering :) antecipate it :) )
Before disconnecting the Windows Server, you should take into account some hidden things that the windows server might be doing besides being a File Server:
- managing windows domains, primary controllers and active directory
- share printers
- email server (by gods sake, if this is the case, then be aware that preparing a linux email server is no small task... and neither is maintaining it)
- login scripts used by windows clients, and delivered by the windows server (it can be done with linux server also, but you will have to do it (see samba))
This is not supposed to scare you, but instead to make you aware and avoid disaster :)
With that said, here comes the good news: linux runs in almost any machine, with much lower requirements than windows servers, meaning you can recycle old hardware to try and make a test linux server without buying anything, and use it to test&convince all other in the office.
The simplest way to start, is to add (not substitute) a Linux Server to the existing network, and create simple services in the Linux Server such as
- File-Server (with samba, very easy, lots of info, can also share printers)
- Chat service (see ejabberd, not so simple, but not that hard)
- Internal Forum for employees (see phpBB, easy to install, up and running in a breeze)
- HTTP proxy (well, better check before promissing anything)
Other services can also be implemented in Linux (and work better than in windows, that's the backbone of how internet works) but they require a more profound knowledge from the system administrator, such as email, firewall, vpn, active directory, primary domain controller, calendar/task sharing, Dns, system monitoring and alerts, ...
I would recommend you start by making a virtual machine (use VirtualBox) and try to make the server there as you intend to do in reality. Also use some linux distribution with which you feel comfortable and there is lots of info/people (big community to search for help), such as centOs or Ubuntu Server
Finally, if you only want to make a simple server-for-1-job, search for a linux distribution which gives you a service and comes ready-to-use, such as FreeNas
Linux can provide a fantastic advantage, when well understood :)
Hope it helps - tell how it went