when you connect to a wireless network in public, there are multiple ways that the network owner or I as a "hacker" can watch what you do or steal your packets.
to overcome this "problem" you want to do something to prevent this risk, a method is to encrypt your traffic in a tunnel, you can have all your clear text or encrypted traffic, tunnel thru the unsecure network and into a secure one.
so if i try to hijack the stream of data from your laptop, i will find that its one big unreadable stream and i cant do much about that other then shut it down.
when i say "trusted network" i mean one that you feel safe on, typically your home DSL or Cable is a trusted network. people don't have the ability to watch your packets there. same with corporate its a network that you feel safe to do work on(or you don't and you buy some hardware for home, i personally architected my company network so i have all the keys and feel safe haha)
here is some cheaper links to consumer gear where you can read up... i also provide a wikipedia or two for the education.
**linksys has some nice looking gear (this one is 120$ and looks like it might be sweet but i have no idea of consumer products so this is just a link in the direction not a product reccomendation)
http://www.linksys.com/servlet/Satellit ... 6854480B03-
http://www.netgear.com/Products/VPNandS ... ificationsa ton of information about VPN
http://en.wikipedia.org/wiki/Virtual_private_network