I have a Ethenet broad band internet connection I want to share it through my notebook's ad hoc wireless network. I have WLAN mini card in my notebook with windows XP SP2

Better to get a wireless router. Trying to do this via an AD HOC network can get really messy. You would have to set up Internet Connection Sharing on the PC that has the (I assume USB or Ethernet connection to the cable/DSL modem) Internet connection.

Then you would have to obtain a DHCP address from that PC with the wireless AD HOC connection. This means that the wireless connection would have to be established prior to the start of networking. This is really iffy.

The router will not only improve reliability but also greatly enhance security for your wireless network and Internet connection.