How to View all 802.11 traffic in wireshark

I am having a bandwidth issue, something is using 4-5mb upload on my network.

I let my neibhor use my network, they have 2 laptops. We are all connected to a Linksys 54g wireless router.

There are 4 computers in total, 2 with vista, the others have XP pro. First of all I can’t monitor anything unless I’m physically connected to my router.

When I am physically connected I can only see traffic from my device, can anyone tll me what I need to do so I can see my entire LAN.

Thank you.

D