Internet Explorer & Javascript logins

Hello

I created a web page which allows customer’s to login to obtain customer price lists. Some customer’s get a word doc and others a pdf. If a customer uses Mozilla after the username and password is entered the right doc opens. BUT with IE versions a 2nd and sometimes 3rd login box appears and requires input b4 eventually allowing entry.

Why is this and how do I stop it happening????

Have a go with either browser at www.cellular.co.nz/test/customer-login.htm

username: test
password: test

If it works it will give u a word doc.

Please let me know how you get on.

Many thanks
Bruce