For the average user who wants to eliminate the risk of someone coming along with a wireless enabled laptop and trying to piggyback their wifi, good practice and the first line of defence is always to stop the router broadcasting the SSID
The second step is to use WPA and not WEP security. The advantage that WPA has over WEP (which was cracked in 60 seconds) are
1) Length of IV is now 48, comparing to WEP’s 24. This gives you over 500 trillion possible key combinations.
2) IV has much better protection with better encryption methods. This is prevention of reuse of IV keys.
3) Master keys are never directly used.
Support for WPA security encryption was introduced into Windows from XP service pack 2 onwards. Anyone still running service pack 1 or earlier versions of Windows should ideally upgrade
As for packet sniffers there are 2 types. Packet capture and packet interception. Packet capture requires that router security has been breached and interception does not. Interception is rather more specialist and represents the danger in airports and other public wifi areas which is why you should always protect your personal data and encrypt your traffic by using a VPN in these areas