[Confused]

You will need ICS if both PC's need to address the network. Only way both can address the network thru a switch is if you have two IP addresses.

Think of it this way. you have to have a address to get on the highway. This address is assigned by your ISP. A second (or third, fourth) PC can get on the highway if there is a means to obtain additional addresses.

That is where a router or ICS comes in.

A router has the address assigned by your ISP and in turn assigns virtual addresses to each PC connected to it. A switch doesn't assign addresses, it just routes traffic to proper PC by using the IP address.

ICS does the same thing. The gateway PC (the one connected to modem) has the assigned IP address and in turn assigns a virtual IP address to its client.

If you read many of the threads in Networking, you will find that ICS will work but can be a huge pain for some people.
Chas