How do I block others from using my router without a password?D-link 802.11g\2.4GHz

You can do MAC (ethernet) address filtering. You can set it to allow only specific MAC addresses to be granted access. For Windows PCs, you can get the MAC adress by firing a command prompt and typing 'ipconfig /all'. For WM, go to 'Start > Settings > System Information' (or something equivalent) select the network section and take note of the Wi-Fi card's MAC address. Anyway, with the MAC adresses of all the devices you want to grant access to your network in hand, navigate to its Web Utility (if it has not been changed before, the IP address is usually set to either 192.168.0.1, or 192.168.1.1, or 192.168.2.1). There, under the security section, you should find the MAC address filtering function.
Please, let me know if you need further details.
Regards, Carlos