How can i share my broadband connection more than one computers? I m using Microsoft WindowsXP Professional?

You can share the connection by using LAN (Local Area Network). If you want to connect two computer, then there is no need for the Switch instead need three LAN (Network) cards on Computers. The structure would go as -

1st computer (say Master) has internet connection through one Lan card (if your modem (router in many cases) provided by ISP, has USB connectivity then there is no need for an extra LAN card).
Share two computers with Crossover cable in their LAN cards. But in this case the 1st computer (Master) must be ON to share the net on other.

If you want to share internet in more than two computers, then you need to setup a LAN (One Switch and LAN cards on each PC with normal Network cables) and just connect your modem (router in many cases) provided by ISP, to any one port in the Switch.