Firstly assumptions, DSL was not mentioned in this thread. hmmmm how come there's a question regarding indian cable networks in the New Zealand wireless networks forums?
It sounds like your ISP provides you with a PPP over Ethernet connection for your Internet access and has some how created a special form of multi-link routing or something between the two PC's, why this conclusion? Logging on from both PCs sounds like each machine gets it's own public IP address, similar to cable in Canada and other corners of the earth, like India (which that IP seems to belong to on the home page). A lot of cable providers require special routers and/or software in order to issue public IP's to multiple PC's over the same ethernet device, so I would strongly ask your ISP's helpdesk as to what hardware you can or can not use to share the connection.
We're not fortunate enough in NZ for domestic broadband to offer IP bridging little own ethernet to our door to start with. We're still catching up with fibre to our doors come 2012.
Cheers,
Gavin.