Networking Wirelessly

I have three PCs.  One wired and 2 wireless.  All connected to the internet through the wireless router (the wired one via ehternet cable) and than through the cable modem. 

 

Since I had to replace my hard drive on one of the wireless PCs, I can no longer print to the printer hooked up to the wired PC.  I tried to add the printer to the laptop, I know the name of that PC, the printer name and confirmed it allows sharing.  On top of that I cannot remember ever seeing any of the other PCs in my wireless network before the crash.

 

My question is if you access the same wireless network, by default are your PCs networked?  And if I am not seeing the other PCs is it because of something like a firewall turned on and it's denying me access to the other PC?  Or is wireless networking and home networking 2 independant setups/processes.  I need to be able to print from the laptop and plan on adding a squeezebox to my home network to play music on my stereo via my pc.