That’s like saying how many people would it take to screw in 152 light bulbs. Well, one if they are not busy and it can take a little while. It all depends on what they are doing. One server (or even just a router/NAT box) could handle computers just surfing the net. Add in email and a single exchange server could handle that well (Depending on your uptime needs) If you’re throwing exchange in there, a domain controller server would be needed, but the exchange server could probably run on that. Beyond that is where you have to ask more questions. Is a file server needed, what kind of files (one server would be able to handle occasional document accesses, etc), most of all what applications do you need, those usually need a dedicated server (like database, etc) Hopefully a start, not a lot of info to work off of. (If the load was light, I’d probably have 2 physical servers, one running a vmware instance of domain & exchange, then another on standby for manual (or semi-auto) failover) Probably some shared storage at that. Otherwise if the load is heaver/more critical, it’s cluster time.