ISA Server and Windows Server 2003 Service Pack 2
The ISA Server product team blog ISA Server and Windows Server 2003 Service Pack 2 states that it might be necessary to disable receive-side scaling (RSS) when running an ISA server on Windows 2003 SP2. In fact, according to Jim Harrison it is absolutely recommended to disable receive-side scaling *and* offload support in the TCP/IP stack. How to accomplish that is explained in the Microsoft KB article You may experience network-related problems after you install Windows Server 2003 SP2 or the Scalable Networking Pack.
However, depending on the NIC driver it might be necessary to disable also offloading of tasks to the NIC (DisableTaskOffload) as well as the TCP Chimney offload in the stack (EnableTCPChimney). This registry entries are found under the registry subkey HKLM\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters :
Values: 0, 1
Values: 0, 1
Update March 11, 2008: check out http://support.microsoft.com/kb/948496. This disables the "Scalable Network Pack" that has caused so much hate & discontent for ISA administrators the world over. So, add this to your "must include" for any ISA or RRAS deployment that includes Windows Server 2003 SP2.