IPod with Linksys WRT54G router - using NAT?

Hello,
I have a few local PCs and a Linksys WRT54G WiFi router all connected to a common switch, then outward to a network and Internet. A few PCs are fixed IP, a few DHCP. I can administer the Linksys through a Wifi connection, or through a direct plug-in to one of its managed ports.

Now, I have a new iPod, and it connects fine to the Linksys and Internet.
But, it cannot seem to see any of the local PCs on the same switch and local network, and vice-versa.

I'd like them to all look like they are just as if hardwired, and be able to interact, even though the iPod is WiFi only. I'd guess that the Linksys is somehow filtering /firewall blocking traffic? Or NAT masking addresses?