Just wanted to quickly chime in that "hiding" your SSID does not really do much for security. Only one instance where the name of your wireless network is broadcasted is hidden. Anyone with the right tools can still find out, one, that you are running a wireless network, and two, what is the "hidden" SSID. This is because the name is still broadcasted when authorized computers connect to it. Hiding it is useless as a security measure and usually more of a pain for you.
Now having a real strong password for both your router and your network key will protect you from people trying to break in. This means a nice long password, ideally randomized, with numbers, letters (some capitalized), and special characters if possible. Long as in more than 10 characters, the longer the better. Your wireless key should be even longer if you want to fend off brute force attacks. Mine is 20+.
And don't use names, dates, and so on. The best tip I can give you is to use a long phrase you will remember (make one up, no famous phrases please), use the first letter of each word, and mix it up. Capitalize some, change others to special characters, etc..
Also make sure to turn off WiFi Protected Setup (WPS), its been proven to be vulnerable to exploitation. Enabling Spoof Checking under Advanced->Firewall cannot hurt (but there may be a performance hit, not sure).
Finally, check now and again for firmware upgrades that fix security holes (if any).