Sophos AntiVirus allows you to either install it on each workstation or deliver it from the server. You can designate a PC as your server, but it will only be able to administer 10 PCs in a workgroup and therefore each time you require multiple installations a new 'server' must be assigned for the new workgroup. This means it is ideal for the smaller business model, but although scaleable may not prove ideal for the larger SME.
Symantec Anti Virus Corporate Edition is an enterprise level solution that resides on your network servers and workstations. It provides a centralized management console, which gives the administrator the means to install the anti-virus protection across the network, update virus definitions and simply manage the solution from the Symantec AntiVirus Corporate Edition server down to the clients.
Vet AntiVirus covers most Windows operating systems so that you can protect this type of environment with relative ease. Making up a reference disk, as Vet calls it, for a boot disk if you are doing a completely new installation is a prerequisite. But the documentation is pretty thorough and walks you through the process with ease. Where you already have a resident anti-virus solution in place this must be disabled prior to starting your Vet AntiVirus installation.