Hi there,
PPPoE (PPP over Ethernet) or PPPoA (PPP over ATM), are quite similar but use different protocols. Both require username and password to sign in.
The main difference is that with PPPoA more work is done at hardware level and thats the very reason we require a modem that supports it.
Whereas PPPoE works via the 1483 Bridged driver and client softwares are used to manage the sessions. ALso for this reason the computer resources are slightly used for a PPPoE connection, u might not notice that.

Thx,
~H*A*R*I~