Pinger,
First, you need to understand that there are differences in terminology between the Windows computers and your Mac. Let's establish that we're really talking about two different things, here: your physical network, and the logical protocols used to communicate across that network.
Windows tends to blend these two things into the single term "network." Without making any judgements here about the sensibility of this, let's just acknowledge that it can be confusing, at times. 😉
As you have found, your Mac will automatically connect to the network using either an ethernet cable or wirelessly (see above; we're going to call a spade a spade. Thus, "network" means no more than your physical connection). Any other Macs that are also connected to the network will automatically be recognized by your Macbook, provided they are "Sharing" any services across the network, but PCs are a different story. With PCs, one must create a "workgroup." Only when a "workgroup" is established by one, then joined by the others, will they all communicate properly.
Your Mac knows about Windows "workgroups," though. "DNS" has nothing to do with this; it is merely the method your computers use to translate domain names to real IP addresses, and it usually will be set automatically. You want to go to the next "tab," and look at the settings for "WINS." In this tab, you need to choose or enter the
exact name of the Windows "workgroup" that exists on your network in the appropriate field.
Once your Mac knows to join your Windows workgroup, it should be able to communicate with the PCs that are also on the network, and vice versa. You
do not need to turn on "Printer Sharing," "File Sharing," or "Windows Sharing" on your Macbook unless you will be serving any of these things
from the Macbook. In any "Sharing," one computer acts as a "server," the other as a client, and the controls for "Sharing" only cause the computer in question to become the "server." Client access is automatic.
Now, with all of this said, one thing that can make the job of sharing services across your network easier (especially between Macs and PCs) is to use "Bonjour," Apple's automatic sharing and discovery protocol. Your Mac is already set up to take advantage of this, but your PCs will need to be running
"Bonjour for Windows." I strongly recommend that you download and install this on every PC on your network. It will make your life a whole lot easier.
Scott