BleepingComputer.com: Sharing my Internet

OK,

So My fiancee and I just got dry loop service from verizon. We are very nice people , So upon being asked we decided to let our neighbor use our net. Everything as smooth and fine until last night, but before I go into that. Let me tell you how my Net savy girl set up our network.

1. She changed our Protection from WEP to WPA , And our password was a five letter word and five numbers.... Nothing you could ever hack or break. Even with a password dictionary . It would not have been able to be cracked.

So, my girl was on her myspace last night, and we noticed a significant Lag , and decided to check our Gateway Status page on verizon.com. to our dismay we noticed a third party connected to our gateway. It just happened to be a woman that lives down the street, and is a friend of our neighbor. So we hard reset our modem and changed our WPA password, and gave the neighbor a get out of jail free card. Now, here comes the weird part. After we changed our Pass. My girl went to sign in to her myspace. All she does is type the first letter of her email and a drop box appears with her full email address already written out. Well, last night, and this is the first time this happened. When she typed the letter a different and foreign Email came up in the drop box. So natrurally she thought i had a myspace(which I don't even have, I live vicariously through hers) that I was not telling her about. So I wanted to the bottom of this. So I decided I was going to send this foreign email a message. Asking who they are etc. etc. Well, when I was boucing back and forth from verizon mail to myspace to spell the email correctly. I typed a letter again. this not just one foreign mail showed up,but FIVE this time. One was the neighbors Aol mail. One was my girls, and the rest are a mystery to us. So here come my questions.

1. Why is info from their computers showing up on mine?

2. If that showed up on ours. what can the neighbor see, and what does she have access too?

3. why did It show up for the first time last? As Far as i can tell, last night was the first the third party had connected to my net.. Did that have something to do with the leak.

4. I'm giving the neighbor one more chance. If they give it out again, I'm locking it down. What can I do to protect my self?

5. Is there anyway for someone else can appear invisible on the verizon 'my gateway' site? If so How else can I tell someone other than her is on my network.

6. Are there any settings I should have in place when sharing internet?

Thank You

I hate feeling like someone knows my bleep, so I appreciate any prompt responses....