Networking help

been trying for months to get a network up and runing Wireless (wify do’s not want wires around the house )got a bt voyager 1040in one pc and tryed different pci ,usb ones in over pc(linksys ,bt voyager,and d-link ) and tryed linksys ,d-link ,and belkin routers for cable (in UK Telewest blueyonder)put they lose connection with the modem (surfband sb5100i)every few hours.
can get them to see each over put not talk to each over (adhoc)and when i do they stay connected for a few mins and you get the pc’s to talk ,ping each over fine and see shared files put not internet or internet put no shared files or ping each over .
also had a person (brother) that networks for a living come to have a look and he says every thing it set right should work (got him stuck).
the house has plasterboard wall (honycomb )the pc’s are with in 20 feet of each over .
tryed static and dynamic ip’s ,dhcp on one put not over and they pick an over network up that’s faint?.
they work happy then wired crossover lead or patch in a router .
has any one got any idea whats going on or hardware to us has the last lot of hardware is going back tomorrow (16th may)linksys usb network adapters wusb11 ,wireless-b(802.11b).
both pc are home made and only a few months old no more than 6 months .they worked fine on BTboardband with the adsl BT Voyager 2100 Wireless
any sugestion please