Picking Up Someones Signal

i'm on my iBook and i'm picking up someones wireless signal. i'm guessing it's a neighbor. the airport thing on the menu bar says linksys. so i'm picking up someones wireless linksys router?

1) can they get into my iBook or am i protected?

2) if i use their wireless connection what can they see on my end and what can i see on their end? can they get my passwords?

1) Turn on your firewall and have a password and you are fine
2) If you have a password to get on your computer they can't see anything and even if you don't have a password they can't access anything valuable unless you have those folders shared. If they are on a windows pc they can't do anything period

1) if i accessed my mail using their wireless connect couldn't they get my email and password? can't they see what i'm doing over their wireless?

2) my iBook has a firewall? how do i turn it on?

1. No they can't. They can't see anything that you are doing other than the IP address of your computer. That's if they are even smart enough to know how to (if they dont have WEP active then they probably aren't smart enough to even get into the network config)
2. System Preferences -> Sharing -> Firewall

what about sniffers? so can i basically use this persons wireless connection?

Yes you can use. Sniffers? sniffers are people who do what you are doing...go around and use other peoples internet connection

i thought a sniffer was a program that captured everything that came in over a network. like what businesses use.

No personal user has a program that does that. The programs companies use to monitor their workers browsing are very expensive trackers. If the person is dumb enough to not have WEP enabled then there is no way they are using a tracker

Turn on OS X firewall: System preferences, Sharing, firewall = middle tab. Good to go