ISA Integration with Active Directory

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hi all ISA GURUs,
a small question for all, here is how it goes;
I have Active Directory Server running on my network, and ISA 2004 EE working
in flat condition. Now this is what i need to do;
1. The ISA server to be integrated with Active directory server
2. In Rules which ever domain user is permitted for HTTP goes on else is
denied

This is what has happened,
my isa server is repetedly asking fo rlogin credentials and is then not
giving access to authenticated users.

can any one help me out in this situation.?

.