I have not used such an ISP before, but Debian has a method of dealing with it if it is a proxy server your are connecting.
GNOME GUI:
Desktop/preferences/network proxy/
setup manual proxy and click "details", "use authentication" and supply username and password.
CLI:
in ~/.bashrc
edit in
export http_proxy="http://username
assword@proxyipaddress
ort
(smilies inserted somehow... username colon password at proxyipaddress colon port)
port is often 8080 or nothing for transparent proxying.
You will have to log out/in to pick up the changes to .bashrc or your can just run it:
~/.bashrc
To do this for all users, edit /etc/bash.bashrc or /etc/profile or /etc/skel/.bashrc to pick it up for new users.
From man bash:
When bash is invoked as an interactive login shell, or as a non-interactive shell with the --login option, it first reads and executes commands from the file /etc/profile, if that file exists. After reading that file, it looks for ~/.bash_profile, ~/.bash_login, and ~/.profile, in that order, and reads and executes commands from the first one that exists and is readable. The --noprofile option may be used when the shell is started to inhibit this behavior.
When a login shell exits, bash reads and executes commands from the file ~/.bash_logout, if it exists.
When an interactive shell that is not a login shell is started, bash reads and executes commands from /etc/bash.bashrc and ~/.bashrc, if these files exist. This may be inhibited by using the --norc option.
The --rcfile file option will force bash to read and execute commands from file instead of /etc/bash.bashrc and ~/.bashrc.