Look on the back of the router for a small hole. Use a needle to push down on the reset button in there for a few seconds while powered.
You didn't say what manufacturer your router is, but you will have to get to it's config page. DLink's are 192.168.0.1, while Linksys are 192.168.1.1. Don't know about the others. You also have to temporarily give your wireless NIC a static IP on the same subnet.
WEP? If you are concerned about security, you want WPA. Does the router belong to your cable company? If so, tell them to take it back and buy one yourself.
If it belongs to you, and doesn't have WPA (and you are concerned about security), then all you can really use it for is a wired router by disabling the radios and breaking the antennas off.
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