in your original post, you gave a link to "whirlpool.net".
scroll to the bottom of the info page, it gives you 3 default IP options...see which one corresponds with your ISP.
alternatively, on your PC which is connected to the modem, click on start>run then type CMD into the run dialogue box and press "enter" to bring up the command prompt. at the prompt type IPCONFIG /ALL and press enter.
you will now see your IP information. have a look at the "default gateway" address, this is *usually* the LAN address of the device you're connecting too.