Not that we're advocating this or anything, but if you want to get an idea of how insecure Wired Equivalent Privacy
— the most common encryption protocol used on WiFi networks — really is, you may want to check out this step-by-step
guide to WEP cracking thoughtfully provided by the good folks at Tom's Networking. If you do decide to follow their
guide (for purely educational purposes, of course), be prepared to invest a little in hardware (all off-the-shelf
stuff) and to learn a little about Linux. Seems like a small price to pay for the
access to all of your friends' and
neighbors' networks wealth of knowledge you'll gain.