If you've set a WEP password in the router you need to apply it to the Mac. For that you'll need to either remember the password or connect to the router with an ethernet cable and look at it that way.
If you can't find the router's IP address now, it may be because it's connected to a separate modem ? You need to disconnect from the modem and restart the router.
Incidentally, WEP is unsafe and the 128 version produces ridiculously long passwords -- if possible use WPA.
See, I knew the password, and I had connected to the router, and I had the IP address, it just wouldn't take me to Routers page on my browser, but I tried a few things this morning, and sure enough, my net is up and running, and the connection only exists in my house, so I took off our security as we live in the country, there is no need.