How do you configure a wireless router?

I have seen a couple of posts that instruct a reconfiguring of a router in order to set up maximum security.  None of which I have been able to match to my personal situation, which leads me to my post.

 

I have 4 components currently on my wireless network.  A Dimension 2350, an Inspiron 1100, a Latitude D600, and a TiVo (Server/Receiver?).  My router is a Linksys G.  All are able to recognize each other, that is not the problem.  The problem is that the house I live in is in very close proximity to my neighbor's house.  Just recently, my neighbor knocked on my door and asked me what kind of a network I was running because he just got a computer with wireless capabilities for Christmas.  He is picking up my network.

 

I have two questions:

1)  How do I set up all of my components on the wireless network to maximum security and still recognize each other?  I know how to connect all of them to the network, but when it comes to accessing the software configurations and changing the settings, I am not well versed.

 

2)  Is there any way to restrict my wireless network from access to any others except for me?  If so, I would guess that I would not need an answer to my first question.