Your basically confused. You chose a username and password that allows you to connect to a network. This can be used as an email if you like. You might have
[email protected] with a password of "password". Bad choices.
Only the DSL modem needs to know this password. It's a set and forget.
You are then able to set up 5 sub-accounts for email. This allows outlook express to work.
You don't have to use these. You can use Yahoo, AOL or gmail for email addresses. They are portable.
Something called NAT and DHCP allow multiple computers to share an internet connection.
I'm not sure where we are at, so I'm going to stop here.
You could be connecting via USB and having the computer keep track of the PPPOE connection - yuk!
That's not what you want.
Tell us a bit about your setup? How many people? How many computers? Wireless?
What mail program?
At least some idea. How the computers are connected, etc?