Can someone explain basic wireless internet security to me?

[Zippyy]

Don't forget to change your router's admin password from the default:)

I'll add my voice to all those doubting you should tie down MAC addresses - this will make it harder for you to allow other people to connect, for example if a friend brings his laptop round.

Agreed. The inconvenience is not worth the thin layer of security it provides. Bypassing MAC filtering is about as easy as punching through a tissue.