Help: WiFi card and network setup

Could somebody help me with this problem?

I have a compaq x1000 notebook which has a build in WiFi card.

I have a strange problem when using my WiFi connect to my wireless
router, there are more than one computers under the router:

I can see other computers and others can see me. When I click the
other computer, I got network path not found or permission error. Same
thing happens when click from other computer.

The above will not be a problem if I use an phsical cable connect to
the router. We can see each other and we can browse the shared files
or printers.

Anybody know what is wrong?