Say your connection is bound to your desktop's MAC.
Then try this:

1) Install the Sify Client on your laptop.
2) Change all the settings that you got (e.g. gateway, IPs, etc).
3) Change the MAC of your laptop using SMAC to MAC of your desktop
PCWorld Award - SMAC MAC Address Spoofer / Changer for Windows VISTA, XP, 2003, 2000
4) Login.

I guess it should work.