MacBook Air - Cannot connect to Ethernet Computers on WiFi Network

Question

I just bought a new MacBook Air (11 inch) less than a week ago. Love it, its great. I am however having an issue with connecting it to computers on the same network, but only if those computers are connected to the network via ethernet (while the Air is on wifi).
I have an older MacBook (2.2Ghz running 10.7.2 also) with no issues connecting to other computers over the wifi if they are on ethernet. My old MacBook and the Air can also communicate no problem over wifi, but if I connect my old MacBook to the ethernet connection I cannot ping it from the Air.
The reason why this is important is because I am trying to hook the Air up to a buffallo linkstation to setup TimeMachine like I have it set up on my old MacBook.
I am using a Buffallo WZR2-G300N Router as my gateway and access point (I also have a D-Link switch, but I have by-passed that to troubleshoot the issue). Firmware is up to date.
The Air also has no problem connecting to the internets.
Any ideas oh Apple Support Community?? Many thanks in advance.

Answer 1

Try using Finder > Go > Connect to Server > smb://ipaddress. If you can connect this way, then good. I'll have more to say later. Just try to get this working for now.
Before trying to connect:
On the XP machine.
1. Right-click on a folder to share (e.g., My Documents), chose Sharing, and select both Sharing Options.
2. Restart (probably not necessary, but I’d do it).
See how this part goes. I can't remember where some things are in XP, but you may have to enable Network Discovery somewhere.
On the Vista machine.
1. Go > Computer > Users > User; right click on the User folder, and choose the settings that give Everyone—both Read/Write permissions.
2. Go Control Panel > Network and Sharing Options > Turn on network discovery, Turn on file and printer sharing, Turn off public folder sharing , and Turn off password protected sharing (unless sharing won’t occur without turning it on).
2. Restart (probably not necessary, but I’d do it).
See how this part goes too. I can't remember some of the detail in Vista.
On the Sno machine,
1. Go System Preferences > Sharing > Check File sharing > Go Options > Enable SMB sharing.
2. Go System Preferences > Network > Select Airport or Ethernet depending on what you are going to be using. I am assuming you will be using wireless below. Let me know if not true.
3. Having selected Airport, select ask to join new networks and show Airport status in menu bar.
4. Click advanced > click remember networks this computer has joined > Click Wins > Enter the ip address of your Win7 machine in the WINS server box > Enter the Win7's workgroup name in the workbook box unless it already is there (look in the drop down menu too). In all likelihood the name is workgroup, but check on the Win7 machine.
5. Restart