Wireless LAN problems

[Sputnik II]

I've been asked to have a look at a friends network because they have two computers running on adsl internet connection via a dlink router. the first machine is physically plugged into the router using a lan cable and the other one is connected Via wlan, this one is apparently showing it has an excellent signal but, they keep getting dns errors when trying to view web pages.
The router is supposed to be a Dlink dwl-904 but, I can't seem to find any info or existance of a router with that number.
Does anyone know about this model of router or what might be causing this problem? the company they bought this set up from wants £50 per hour to look at it.

 

[Sputnik II]

It seems that the number I was given is for a router /usb wlan dongle. The router number is DSL G604T. They have also said that the company that supplied this system has put them on its own system because the guy from the shop said that BT's system can't handle large numbers
Any information on setting this thing up would be great.

TIA