Tungaw2001,
I have a like setup, two NIC's, one to internal LAN the other to Internet. In my case, the second NIC is connected to an xDSL Modem. So, I am using the ADSL-SETUP script to establish the connection. Here is what I had to do, hope it helps.
Ensure that the Eth1 NIC is not being brought up during the boot. The ADSL-START script will take care of this.
Run the ADSL-SETUP script supplying the values as requested. Note: In most cases the account and password values will be case sensitive.
Once that is complete run ADSL-START, this will invoke the ADSL-CONNECT script. If you set it up correctly the system will return to a command prompt. Try issusing ADSL-STATUS, this should show you the status of the PPPx connection. You could also issue IFCONFIG, you should see all of your interfaces, including the ETH1. Note: the ETH1 interface will not have an IP Address, you would reference the one on the PPPx Interface.
I can tell you that RH9 uses the Roaring Penguin PPPoE product for this type of connection. You can find additional information at the following site. Best of luck....
http://www.roaringpenguin.com
John