What's the difference between a hub and a switch?

[Everything sent through an ethernet network is basically cut into small bits of data known as packets. The computer wishing to send information gives the packets an address, and sends them down the cable.

If the packet comes to a hub, then the hub copies the packet and sends it to every other port it has. Once one of the packets gets to the proper destination, the intended recipient sees their address on the packet and accepts it. Those that do not see their address on a packet, discard. With a hub, if systems try to send on the line at the same time then a data collision occurs and the packets must be resubmitted.

A switch is a bit smarter. It learns the addresses of the individual systems. When a packet comes to it, the switch takes a look at the address on it and sends the packet to it's proper destination without sending it to everyone else too. Due to these improvements over the hub, the switch often performs better where high network throughput is desired. .]

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What is a NIC?

[NIC is short for Network Interface Card. A NIC allows you to connect to connect to a network, or network device. They come in a variety of shapes, sizes, and network support lists. The most common network cards are PCI 10/100 ethernet network cards in desktop systems, and PCMCIA 10/100 ethernet cards in laptops. NICs can be integrated into a motherboard, or other device. This may be referred to as Onboard LAN]

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What is a Firewall?

[A firewall acts as a middle man between you and the internet. It looks briefly at the packets going into and out of your system, and gives each one a thumbs up or thumbs down verdict. (pass or block). This action helps prevent outside intrusion attempts on your system. Firewalls come in two forms: Hardware and software. Software firewalls operate on a system and run in the background monitoring your connection. The may be called "Personal Firewalls". Hardware firewalls are separate boxes that do the work of a firewall without taking system resources. Almost all routers contain at least a basic firewall functionality.]

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What is NAT?

[NAT is short for Network Address Translation. In a nutshell, NAT allows a group of computers to use a single IP address to communicate with the outside world or another network. Additionally it separates External IP addresses from Internal network IP addresses.

A device or program using NAT sits between the Internet and the network. It rewrites IP addresses and port numbers on the fly so every packets appears to be coming from (or going to) the single IP address of the NAT device instead of the actual source or destination. This allows more then one system to access the Internet at the same time, and it allows a measure of safety as the outside site never sees the internal IP address for the system it's sending to. In this way, NAT also acts as a simple firewall.]

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How to configure a computer to connect to more than one network?

[If you have WinXP and need to configure the computer for two independent connections, Windows let you configure two TCP/IP stacks.
Click on Control Panel / Network Connection, and right click on the active Local Network Connection to get the properties.  Choose the TCP/IP properties then the Alternate Configuration, and configure it with the entries pertaining to your second Network.]

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 How can I keep the same IP for each network device?

[While keeping the same local IP is a good idea for all Networked devices it is an utmost need in case of Networked Devices that are used by all the computers on the Network (Network Printers, or Networked Storage units).

If the IP of the devices mentioned above changes often the Network would work slow down and sometimes the devices would not be found at all.

In general there is two ways to assign a specific IP to a specific computer, printer, or other Network device.

1.  Assign a static IP in the Device's TCP/IP Properties.

2.  Use a Router that can do IP reservation within the DHCP (aka Static DHCP). Static DHCP means that the network device can be set to Auto Obtain IP and it would be always assigned with the same IP number. 

If your Router can do Static IP,  the computer's TCP/IP properties should be set to Auto Obtain IP, and the Router can be set to provide a specific IP within the DHCP range to be reserved for a specific computer/device according to the computer/device's MAC address.  Read your Router’s manual for the specific setting.

Please note that providing this feature is not common to all Routers.

As an example most of Netgear Routers can do DHCP Reservation, while most old Linksys Routers cannot.

If this is an important feature read the Router’s manual before you buy. Almost all Routers manuals are available as pdf download on the manufacturers support site.

Note. Static IP,  DHCP, and Static DHCP can be use at the same Router as long as the Static IPs are not within the range of the DHCP server (Read your Router manual to find what is the default setting of the DHCP).

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