the wireless security is somthing you set in the netgear itself not the wii, you need to open up the web page for the netgear
meaning open up a web browser on a computer that is connected to the router. in the address bar put in 192.168.0.1. that will open up a page for the netgear itself- you are literally looking inside your router. if it asks for a user name and password it is most likly username= admin and password= password
after that look around the web page for wireless security and look for where it asks for a wep key- from there you can usually enter a paraphrase and it will create the wep key for you.
once you set the wep key write it down, you will then need to go back to the wii and reconenct it to the router- it will ask for a password- enter the wepkey and it will then connect to the router
by creating the wepkey no one will be able to connect to your router unless you give them the wepkey and as for hackers and the such the router is already acting as a firewall against that
hope this wasn't to confusing, if it was let me know