BackTrack is ubuntu based, So i want to share my problem here !

I am using wired connection. ISP has given me a username , password and they noted my mac address.

I have configured PPPOE connection by pppoeconf using my username and password. it works fine when i connect through my main laptop lan port. When i connect through usb ether-net port and reconfigure it shows eth1 [installed].

But the main problem is my mac address. since my usb ether-net MAC is different i can't use internet.

so i have to use my main Mac. i have changed mac from
Code:
/etc/udev/rules.d/70-persistent-net.rules
.
but when i want to configure / restart it creates another one with its own mac.

i downloaded Network manager , but i cant fix it.

is there any way to make connection through my Ether-net usb device in UBUNTU / Backtrack.

Please Help !!!!