Windows 2003

I am sorry writing in English I have no Arabic key and I will reply in simple words

As you know there are two types of networks, workgroup 2-9 PCs and domain controller with Active directory to more than 10

AD contains main network objects, users, groups, computers, printers and share... so when you create one of these objects, its enough to access your network, you don't need to create this object on each computer

The key here is all centralized

Cluster Service used for high availability, to create cluster you need 2 nodes, shared storage and windows cluster service. After the installation your service may run on one node, if any failure on first node the second one will handle the service