If you have Vista's User Account Control (UAC) turned on (the default), you may need to start the Command Prompt in Administrator Mode in order to perform necessary Command Prompt procedures.
Click on the Start button and then on All Programs.
Click the Accessories menu.
Right-click on Command Prompt and then click the Run as administrator option from the pop-up menu.
If Vista's UAC is turned on, click the Continue button.
The Administrator: Command Prompt window should open.
When you are finished using the Command Prompt, close it using the exit command. You can also close it by clicking on the window's Close button.