Here are the steps to turn off Auto-Tuning in Microsoft Windows Vista:

1. From the Start Menu, click Run and type "cmd" to open the Command Prompt window.
2. Type "netsh interface tcp set global autotuning=disabled" and hit the Enter key.
3. The system will return "OK." and you are done.
4. If you want to confirm the auto-tuning setting status, type "netsh interface tcp show global" and hit the Enter key. The system should show the following:
   
    Receive Window Auto-Tuning Level    : disabled 
   
   
    
5. Type "exit" to close the Command Prompt window and done.

Here are the steps to set it back to normal:

1. From the Start Menu, click Run and type "cmd" to open the Command Prompt window.
2. Type "netsh interface tcp set global autotuning=normal" and hit the Enter key.
3. The system will return "OK." and you are done.
4. If you want to confirm the auto-tuning setting status, type "netsh interface tcp show global" and hit the Enter key. The system should show the following:
   
    Receive Window Auto-Tuning Level    : normal 
   
   
    
5. Type "exit" to close the Command Prompt window and done.