Disable RSS & TCP offload manually

For ISA 2006 works properly, Scalable Networking Pack (SNP) feature which enabled by default in Windows Server 2003 SP2 need to be disabled:

To manually disable RSS and TCP Offload yourself, follow these steps:

1. Click Start, click Run, type regedit, and then click OK.
2. Locate the following registry subkey:
   HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters
3. Right-click EnableTCPChimney, and then click Modify.
4. In the Value data box, type 0, and then click OK.
5. Right-click EnableRSS, and then click Modify.
6. In the Value data box, type 0, and then click OK.
7. Right-click EnableTCPA, and then click Modify.
8. In the Value data box, type 0, and then click OK.
9. Exit Registry Editor, and then restart the computer.

If you set the value of the EnableTCPChimney registry entry to 1, the TCP Chimney functionality is enabled. Similarly, if you set the values of the EnableRSS and EnableTCPA registry entries to 1, the RSS functionality and the TCPA functionality are enabled.