Belkin wireless G range universal extender /access point

I have just bought this G range and just find it inpossible to get connected to my wireless system as i need to have better coverage around this very large Property. Belkin have tried and just left me to cope with this problem as they havent phoned back as promised two days on and still have a fity pound box of equipment and need to solve problem or return goods to PC World. My thought for this large property were to have two of theses Extenders with the router . I have a router also Belkin G+Mimo bought same time a week ago as the universal extender was bought and Belkin helped install that Router and all is ok ' but i have very low coverage with the Router' and thats the problem also. But no way can i get this Extender to work in line with the router and it seems as Belkin them selfs are in dificulties as to what to do. Please can one of you Smart Guys help me as i have spent hours on the phone Yes hours to Belkin being posted from one department to others and feel that i need straight faward help with this Wireless G range equipt as i am reasonably new to compts and need a system that will cope with more than just one or two desk/laptop compt as i mentioned to Belkin and also to Virgin Media who put me onto John in the C/Service dept/ Tec and he was very very helpfull and polite and gave all support to my prolem as regards Belkin and the lack of responce to this problem and getting it solved. I have Xl speed into the property and understand it is a problem with the set-up of the Belkin wireless G range extender only and not Virgin Media. Well if you thik that you could help i will be very gratefull for your help .