Does that site give you the option to save password? I generally would not recommend using that feature for security reasons but, in this case, it might be a good choice for you if the option is available.
For username, have you checked to see whether IE remembers most recently used usernames? If you open your browser to that website's logon page, put your cursor in the username box, and either click again or hit the down arrow on your keyboard, do you see your username in a list of recently used usernames?