Look on the back of 713P. There should be a small hole, usually just to the left of the power jack on DLinks. Inside that hole is a small button. Find something small enough to press and hold it while the 713P is powered up. While pressing and holding, watch the lights on the front. With DLinks, its usually the M1 and M2 lights that will go solid while holding the reset button. Keep holding the reset until they start blinking. Its now reset.
To reconfigure at 192.168.0.1 after it is reset, you can either do it over-the-air (SSID will now be "default" and unencrypted) or by connecting a CAT5 cable from your laptop to one of the 713P's LAN ports. Does the 713P have DHCP enabled by default? Its likely that it does not. All of my DLink stuff, by default, has DHCP disabled. If DHCP is disabled by default, you'll have to manually enter IP's under TCP/IP properties for whatever network device you are using to connect with it (wireless card or NIC). Choose an IP in the same range, such as 192.168.0.100 and set the broadcast address to 255.255.255.0. Don't worry about the gateway and DNS addresses, this is just for getting out on the internet. It doesn't need them just to talk to router. Point you browser to 192.168.0.1, turn on DHCP and apply any other settings you want. Change the TCP/IP settings of whatever network device you used to connect back to "Obtain addresses automatically" and it will now pull IP, broadcast, gateway, and DNS.
BTW: MAC filtering doesn't really offer that much in security. MAC addresses are easy to obtain (even when using encryption, MAC addresses are sent out in clear text) and spoof (changing a registry value!). It'll keep out those that don't know how to spoof MAC's, but if someone is taking the effort to crack your WEP (I'm assuming the 713P doesn't have WPA), I'm sure they'll know how to spoof a MAC as well. The question becomes, is the extremely thin layer of "security" with MAC filtering worth the extra annoyance it bring you?