Is this a normal Business enviroment to have all tasks on one server? And am i just in the dark here (being used to Win2K/2k3) and having multiple machines dedicated to certain tasks?
All depends on your requirements (and your customers), but you have 4 servers and only use one? If that one breaks, you're complete out of business
I assume you have hosted your servers in a external datacenter and you have at least one public IP address per server. If not, you're more or less stuck to one server. You should at least use two servers for DNS. You can split web serving and mail handling on different servers. You can spread different websites across different servers (E.g. I have different servers for a Perl based CMS and PHP based websites). That way you can share the risk of failures and having a server crash will not put all your sites and services out of order. Setting up a real business environment is a complex task which requires a lot of planning and careful usage of resources.