How to configure 3 linksys wrt120n router? please help me... thank you.

please go through this link to configure PPPOE on your router
http://kb.linksys.com/Linksys/ukp.aspx?vw=1&docid=9017a6f6bece444dbb4a0746eb87682a_2210.xml&pid=96&slnid=3

To connect to your wireless router, the router's wireless settings needs to be configured with the SSID, encryption etc. and also the wireless cards in all the laptops/computers needs to be configured with these router's wireless settings. Then the laptops/desktop computers can communicate with your wireless router.
Connect a LAN cable from the Linksys to the LAN port on your computer.
Open a browser and enter the Linksys configuration URL
http://192.168.1.1
The default login = admin
The default PW = admin
You can protect your router by changing the default admin PW (write it down and put it in a safe place)
Go to the wireless configuration and set up the SSID and WPA or WPA2 encryption.
Now apply these settings to the wireless card in your laptop/computer.
To secure your wireless network from unauthorized access, please click on this link and follow my instructions :- http://www.fixya.com/support/r3559128-wireless_router_security

To connect to your wireless router, the router's wirelesssettings needs to be configured with the SSID, encryption etc. and also thewireless cards in all the laptops/computers needs to be configured with theserouter's wireless settings. Then the laptops/desktop computers can communicatewith your wireless router.
Connect a LAN cable from the Linksys to the LAN port on your computer.
Open a browser and enter the Linksys configuration URL
http://192.168.1.1
The default login = admin
The default PW = admin
You can protect your router by changing the default admin PW (write it down andput it in a safe place)
Go to the wireless configuration and set up the SSID and WPA or WPA2encryption.
Now apply these settings to the wireless card in your laptop/computer.
To secure your wireless network from unauthorized access, please click on thislink and follow my instructions :-http://www.fixya.com/support/r3559128-wireless_router_security

I think you can try upgrading the firmware on your router,

Connect the computer to the router.
Download the latest firmware.
Open the setup page of the router and upgrade the firmware.
After upgrading the firmware, reset the router and reconfigure it manually.

See How to upgrade firmware on Linksys router.

Watch video: Linksys router setup

Looking for the Linksys WRT120N default password? You probably have little reason to access your router on a regular basis so don't feel too bad if you've forgotten the WRT120N default password.

However, when you're troubleshooting a network problem and need to get in to the device, the WRT120N default password suddenly becomes very important.

For most versions of the Linksys WRT120N, the default password is admin. As with most passwords, the WRT120N default password is case sensitive.

In addition to the WRT120N default password, you can also see the WRT120N default username and WRT120N default IP address in the table below.

Note: The Linksys WRT120N default password may be different for certain hardware orfirmware versions.

If I have that information, I'll include the exact WRT120N version number along with the correct default password. You can usually find your Linksys WRT120N version number on the bottom of the router.

Be sure to change the default router password on your WRT120N to something more secure as soon as you're in. Then use a free password manager so you'll never forget your new WRT120N password.
Help! The WRT120N Default Password Doesn't Work!

At some point during the life of your particular Cisco Linksys WRT120N, the default password, username, and/or IP address might have been changed.

In most cases, if the Linksys WRT120N default IP address has been changed, the new IP address for the WRT120N will be the same as the default gateway IP address configured for your network connection.

See How To Find the Default Gateway IP Address for help.

In situations where the WRT120N default password or WRT120N default username has changed, you'll need to reset the Linksys WRT120N to factory defaults. You can usually do that via a special button or sequence of actions.

The WRT120N manual will have specific directions for performing a factory default reset. You can download the manual for the WRT120N from Linksys Support.

Please let me know if any of the WRT120N default login data below needs updated. For other questions about the WRT120N default information on this page, see my Default Password FAQ.
WRT120N Default Password & Other Default Login DataVersionDefault UsernameDefault PasswordDefault IPPrivilegesAll[none]admin192.168.1.1Administrator

This is too involved to just post your router settings. I would recommend reading up on how to "cascade" your router or to make your Modem/Router act as a bridge.

The dlink will need to have its DNS disabled and have the Linksys do the DNS. Then the LInksys will be using the Dlink as its host. you may be better off seeing if you can make the dlink run in Gateway mode instead of router mode.

Then see how to implement the cascading router with your particular situation and WAN IP.

Use the on line guide from this link. It's very easy to configure it.
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Stelios
direct fixya link: http://www.fixya.com/users/technical114

Here is a direct link to show you how to change password and secure resecure router you will want to reset your router before configuring simply press and hold reset button for 15 seconds until router resets. click on the link below to secure your router good luck.
http://www.wonderhowto.com/topic/linksys-wrt120n/

the wireless part is not configured yet....

You can have a look on this link....so that you will get an idea how to configure the wireless part....