See if Windows Internet Connection Sharing will work. Link the two computers via their ethernet ports (either with a crossover cable or via the switch you mention). Turn off firewalls. See if ICS will allow you to share the internet from the Airtel card.
Bear in mind that ICS can cause problems because of the way it uses an IP address.
And it is not particularly reliable.
The way most cards like the Airtel connect to the computer by PCMCIA or USB rather limits their usefulness -- there are now cellphone internet routers which allow proper sharing. I believe they are still expensive.