Squid on Linux Windows Pass through authentication

We are setting up a new proxy based on squid on an ubuntu server, and would like to have pass through authentication work for the Windows/Internet Explorer client.

We have put the line into the squid.conf for squid_ldap_auth, but this prompts for a username and password in internet explorer. It does work ok once the user puts it in.

Whats the 'best' (standard) way of using pass through authentication?

Cheers Luke