Using NAT you can have a number of machines with different IP addresses talking to the world wide web through one IP address. A router that is NAT enabled (which is most of them) analyses data as it passes from your internal network out to the WWW, and stamps it with the IP address of the originating machine. It also stamps your static IP onto it, so that the web can send it back to you. Once it returns it still has the original machine's IP stamped on it so your router knows where to send it. So all you really need is a NAT enabled router; connect your internet connection into it and connect your machines to the router via a switch. As you have 4 public static IP's what you need to consider is the ability of your router to handle multiple static IP's, and how you are going to split the network between these public IP's.

Using NAT you can have a number of machines with different IP addresses talking to the world wide web through one IP address. A router that is NAT enabled (which is most of them) analyses data as it passes from your internal network out to the WWW, and stamps it with the IP address of the originating machine. It also stamps your static IP onto it, so that the web can send it back to you. Once it returns it still has the original machine's IP stamped on it so your router knows where to send it. So all you really need is a NAT enabled router; connect your internet connection into it and connect your machines to the router via a switch. As you have 4 public static IP's what you need to consider is the ability of your router to handle multiple static IP's, and how you are going to split the network between these public IP's.