Hi, The easiest way is to set encryption mate, one method of encryption is called WEP “for ten year old talk think of this a as password” actually does a lot more than this but if you think it is just a password you will be able to set it up and secure your network
Heres what you need to do:-
On your router you should see an option for wireless, then security then WEP. Select WEP and key in a set of characters between 0 – 9 and A – F. doesn’t matter what it is as long as you conform to the rules (should be ten characters long)
Disconnect your laptop from the wireless network then reconnect, you will be asked for the encryption key which is the same as you set in the router.
Have a look at the following link before you set it up. Hope this helps
H**p://www.practicallynetworked.com/support/wireless_encrypt.htm
Capdan