Windows Vista won’t automatically create ad hoc wireless connections with other computers, but for greater security you may want to disable ad-hoc wireless connections entirely. You can do this by running the following Netsh command at an elevated command prompt:
netsh wlan add filter permission=denyall networktype=adhoc
To re-enable ad hoc wireless connections, run this command:
netsh wlan del filter permission=denyall networktype=adhoc
For more information on networking in Windows Vista and Windows Server 2008, see the Windows Server 2008 Networking and Network Access Protection (NAP) from Microsoft Press.