Depends on if you want to play nice and whether you're in an area that has an 802.11 b or g network. In that case you can just check the drop down menu on your AirPort signal indicator to see what you can get. If you see anything, try connecting to it. Yes, there are ways to try to steal passwords and such, but that's too technical for most people. Plus there's that whole thing about being in an area where there's an 802.11 network. This is usually only realistic in a downtown area. If you're lucky you'll find one in a residential area, but don't count on it.
Now, if you want to connect from almost anywhere just forget about AirPort. What I use for that is a Bluetooth connection to my cell phone. To do that you need a phone with Bluetooth and some sort of data plan, which could cost anywhere from free (unlimited from T-Mobile) to $50+ for unlimited, depending on your carrier. This solution will work in just about any city. Getting connectivity in more rural areas is possible as well, but will most likely require that you use some of your wireless minutes (in cities it would subtract from your data plan, not your minutes). If you want more info, try searching the forums here, or Google. Another good resource is
www.howardforums.com. A search there will help you set up everything once you have the phone and the data plan.