the best way to use bsnl broadband is thru ethernet and bridge mode. if u dont have a ethernet card get hold on one, they are pretty cheap.

after that if u have dhcp enabled just plug in the ethernet cable ur ubuntu machine shuld take care of the rest. If u dont have dhcp enabled u need to manually configure the network address, netmask and gateway.

@ starting ubuntu
ubuntu has evolved a long way from wen i first started using it some 4 years back. for one it has become much more user friendly.
for all those who are starting ubuntu the first things ull notice are
1. fast booting and shuting down time(boots less than 30 seconds falt even with hundreds of software)
2. superior graphics ( aero pales in compariosn)
3. faster file copy and all
after that connect to interent
go to systerm -> administration -> synaptic and enjoy ubuntu