Stop others from using my wireless internet

I want to make it so my neighbors or others cannot use my wireless internet connection.
My Setup: Linksys WRT54G with 3Pc's hard wired ,laptop thru wireless and a DVR that gets the channel Guide thru a D-Link DWL-G739AP wireless. WAP enabled in router.
Is there a way to require a password to access the wireless connection to the router and still allow the D-Link AP to get the channel guide thru the router. I can't put in password on the DVR or AP. Right now the DVR gets the channel guide automaticly whenever it needs it, and anyone of my relatives that brings a laptop can hook to my internet.
I'd like to keep everything as is , just retrict the wireless connection.