I have a laptop connected to internet through broadband connection via ethernet cable from router. I want to run internet on another computer(desktop), So that I can use internet on both simultaneously. How can I connect both the system to internet without introducing a new device. [My router has an additional USB output besides ethernet output]
Get a switch or router. What you probably have is a cable modem, and without having multiple ethernet ports on it, there isn't really an easy way to do it. The $20 it would cost to get a switch at a local electronic store would cause a lot less headache than setting up an ad-hoc wireless network (if both computers have wireless, if not you would have to spend even more money on a wireless adapter) and setting up internet sharing. Plus, with internet sharing you have to have both computers on for it to work on the tethered one, which may or may not be an issue.
The extra USB port is an either/or, not both. You could use Internet Connection Sharing, but really, I recommend that if you can somehow, just get an intermediate wireless router with an incorporated switch. Windows 7 has removed this feature, so you need to use the other computer to be the primary if it is running Vista or XP.
The easiest thing to do to get two machines online with the same internet connection is to just hook a switch up to your modem and attach a separate Ethernet cable to each machine.
Here is a simple switch example: Linksys EtherFast 10/100 5-Port Workgroup Switch EZXS55W Switch - 5 ports
No configuration is needed for either the modem or the computers. Just hook the cables up and you should be good to go.
Hope this helps some.