Ubuntu 12.04 - System does't see computers in network

view story

http://askubuntu.com – We have two networks - WLAN for internet and LAN for our office, and we have an interesting problem. My friends computer can see me over network, but I cann't see his computer and cann't access shared folders (all setting are on default). What is there to be done, so I can see his computer over network? (HowTos)