From: Joe on
Ad-Hoc is a wireless network that doesn't need a WAP. Infrastructure mode wireless networks generaly connect to one or more WAP's connected to a wired network, intranet or internet. As far as accessing to crear an Ad-Hoc connection in Vista Go to Start, Control Panel, (Classic View) Network and Sharing, then under the side bar "Tasks" click "Setup a Connection or Network". As for XP go here http://www.home-network-help.com/ad-hoc-wireless-network.html and follow directions.

Hope this helps ..JF