Securing my internet connection, neighbors using it...

My internet connection keeps timing out...sometimes it's after 10 mins using it, sometimes it's 30.  I recently found out that at least 1 of my neighbors is using my connection to get on the internet. I looked and sure enough, my connection is unsecured. I have a Netgear, use cable modem.   How do I secure it or make it password protected so that noone outside my home is utilizing my connection?

The main computer is my dell desktop. I also have a laptop and my son has a laptop(only one with windows vista) and I want to make sure those will also still be able to access the internet after I secure.  I also work from home sometimes so I also have a work laptop that I will have to make sure I'm still able to use when I'm working from home..

So is there a way I can secure it or make it passwork protected.  

Thanks