Hi,
Before installing my DIR-655 I had a Siemens Speedstream 6250 and I could see all my computers (wired or wireless) in the Network Neigbourhood from all my computers.
Since I replaced this router by a DIR-655 a wireless computer can only see the other wireless computers in that Neigbourhood, and a wired computer can only see the other wired computers.
This is not a file or printer sharing issue because by typing the IP address or netbios name preceeded by \\ of whatever computer running in my network (wired or not) I can acess the shared directories or printers in Windows Explorer. I also have a shared printer behind a DPR-1260 and all computers can print using this wirelessly shared printer.
My NAS, wire connected, is only visible in the Network Neigbourhood from other wired computers but accessible from wireless computer using \\<netbios name or IP address> in the address field of the My Computer window.
That's why I think it's a router, or router configuration issue.