You will have to set your router to either 64-bit or 128-bit WEP. This isn't as secure as WPA, but is still secure and will keep out pretty much everyone but the most dedicated of hackers. But if you feel paranoid about l33thackerz crackin into yo mainframes and databases, I would suggest you enable MAC address filter and maybe hiding the SSID (this will make it harder to add new things to your network later on, but still super super basic stuff)