I assume it's ADSL eg uses a BT line to carry the broadband. In which case it setting the username and password to logon to the Broadband service.
With BT in the username you don't just put you Email address but you have to add the gateway code.
so if you email was
bboop@btinternet.com you'd enter something like
bboop@hg01.btinternet.com
The only of difference I know of is with AOL where one of the settings is different to everybody else. I'm trying to remember .... I think it's MTU = 1500 ? It's a long time since I last tried to set up AOL for anybody I haven't have a lot of success. But again this could be down to the gateway code being wrong.
I've done a couple on BT accounts and their software simplified things.
Cable is normally plug and play. Plug the Cable modem into the WAN socket and clone the MAC address using the built in function and away you go.
I think the TP-Link Wireless router I've got is ADSL as I couldn't get it to set-up with the cable modem so it's fed off my Linksys router and does a great job this way. I had to change the IP address of the TP-Link to prevent problems with both routers by default having the same addresses.
Port Forwarding through two routers is fun if you want to use Peer-to-Peer software like Torrent.
And as extra security despite having the firewalls in both routers turned on and WPA encryption with the wireless beacon turned off I've used a function that filters the MAC addresses of computers than can use the wireless signals.So if the MAC address isn't listed in the router you can't access the Internet.
The chap from church may know what I'm going on about ,some of it might be useful.
Hope you get it sorted soon.