Problem with internet connection in Ubuntu 10.10..?

I tried connecting my BSNL nic card(Linktop U100 USB modem) in ubuntu 10.10 by the usual procedure,i.e choosing the mobile broadband connection,setting bsnl as provider,then setting username and pword. The problem is after showing 'preparing to connect',sometime later it shows "you are offline,network is disconnected". I have a dual-boot system(windows7-ubuntu 10.10). I have successfully installed nic in windows 7 and use it.Please help me friends...