scratch the war driving. if you can't even get it setup then war driving is a bit outta your league yet.
does your powerbook have the airport card in it? If not then you'll need one. I am unsure if all 17" pb's have come with airport.. maybe they have, not sure.
Next, System Preferences->Network
Click Airport and click Configure.. it'll change to another screen and it should say "Connect Automatically"
Another way to do this is if you have the Airport icon in the menu bar to the far right, (To the left of the clock) someone posted a picture of the icon already. I'd almost say that if it does not appear there you probably don't have airport on your powerbook... if you do then you need to configure it by doing what i said above and selecting "Show AirPort status in the menu bar" and that icon should reveal itself. If you are near a network if you click on that it should be listed in the menu that drops down when you click on it.
War driving is using a program that searches for open unprotected wireless 802.11 signals. if they're unprotected (no encryption, are broadcasting SSID, and not filtering by mac address) then you can freely connect to the network and use it... as someone stated, sometimes these free networks display a webpage if you try to access without a login/password, in which case you'd have to sign up with them in order to use that particular wireless access point.
You cannot just "get" wireless anywhere.. there has to be a wireless router within a very short distance (100 feet or so in my own personal use.. more if they use better anntenna's).. it's not like a cell service and you just "get it"..
check to see if you have an airport card first and go from there.