We had an issue between isa 2006 and the Windows 2003 service pack 2.
We firstly installed isa and then the SP2. It worked out. The Array was working with nlb, AD replicating between the two nodes.
We then built another time, but firstly the SP2 and then ISA 2006...Nothing working after installing isa...no Active Directory communication, even with the famous any/any allow.
Disabling the RSS changed nothing. It was complaining about syn packet missing (which is wrong).
We finaly built it again, after trying to remove the service pack2.