My brother connects by wirelles lan usb modem. Can we share two computers on this connection? the next computer is about 500 meters apart ? Thank you

unless you have a huge boost or a couple wireless acess points to bring the bridge to ur 2nd computer no because 500 meets is too far... an avg connection can have 300 FEET which is about 100 meters and only 25 meters in doors...

Ok, if these 2 pcs are now connected with 2 different wireless usb lan modems, why cann't these 2 pcs see each other and share any files, i mean there is not "my network places" to see what is in our network neighborhood !! so how to share files ?? thanks

Each LAN, regardless if it's wireless, ethernet, or what, builds a client/server relationship based on a range of local IP Addresses. For most routers this is the range 192.168.0.1 - 192.168.255.255. There are other "local IP Address ranges" defined in the RFCs that could be used but this is the most common for home routers. Every client on a LAN has a local IP address it gets from the DHCP server built into the router. Every datapacket the client sends is "signed" with its IP Address. By default routers will not accept data packets from clients on other LANs. These have to be sent through a "gateway server", which "wraps" the packet in it own, public IP Address. This is by design so Local Area Networks remain "local". Otherwise I could peek into your LAN from my client and vicy-versy. To link two LANs disable the DHCP server on one of the routers and set its gateway address to a port on the other router. Then it becomes a "client" of the host router, it acts like a network switch, and local IP addresses are assigned to all clients on that subnet by the host router. How you do that depends on the flavor of router you're using; check the manual or call the support desk.