I'm not sure that if you mean Microsoft Small Business Server (SBS) or just any server that you can use in a small business environment.
To centrally manage user accounts (specifically Windows accounts) you want to have a domain. For you to have a domain, you need a server running a Windows Server Operating System (e.g. Windows Server 2008 or Windows Server 2012). This server will need to be setup as a domain controller. This role means that it will run active directory services which is what maintains the central user database for your domain. Each computer is then joined to your domain (this is only possible with professional, enterprise, and ultimate Windows Operating System versions). That way each user has a single username that can be used to access any of the computers joined to the domain.
If you mean Windows Small Business Server when you use the term SBS, please understand that is a Microsoft solution that includes Active Directory and Exchange (mail server) in a single server. If you need a mail server, then a Windows SBS server may be a good solution (of course with Office365 the you might prefer to have Microsoft host the exchange server instead of you maintaining exchange too).
If you just need to be able to manage local user accounts (the accounts are stored on each computer not on server) then you can use Microsoft Management Console to manage local user accounts on multiple computers so you don't need to physically go to each computer to manage users, groups, and permissions.
To use Microsoft Management Console, please perform the following steps:
- Click Start
- Type MMC
- Click mmc.exe
Now you need to choose what aspects of your computers you want to manage. Click File, and Add/Remove Snap-in. To manage local user accounts and groups, click Local Users and Groups, then click Add. When you click Add you will be asked if you want to load Local Users and Groups for the computer you are on or a different computer on the network. To add Local Users and Groups on a different computer, select Another computer and type the name of the computer in the blank to the right. If the name of the computer is test you would type \test in the blank to the right and then click Finish. Then you can click OK and you will see Local Users and Groups with the name of the computer it is controlling in parenthesis. You can do the same thing with managing shares by adding the Shared Folders snap-in and Tasks by adding the Task Scheduler snap-in.
Mind you that doing what I described in MMC will allow you to change things on computers without having to go to each one, but what you really want is a Windows domain controller and to join the workstations to the domain so you can centrally manage users, groups, permissions, file storage, and printers. You will need to install Active Directory services, File Server, and Print Server roles on the Windows server you install as your domain controller.