Possible but difficult
>trying to access the internet, provided they enter their correct >username and password they can browse the internet with no >problems.
Normal because Squid use Ldap crendetial to authorize users
>Is it possible to bypass the username/password prompt for >users that are already logged onto the Active Directory Domain, >but still prompt stand alone users for their credentials? This is >purely to cut down on the amount of times a user has to enter >their username and password details.
To have this going on you have to use NTLM authentication on Squid, when a user wants to go to internet IE (to my knowledge only IE can do that) try to identify user with local user/password, this is done by NTLM handshake. Projects exist that provide NTLM authentication for Squid and even NTLM for Mozilla, but it's seem that all of this is not integrated.