1. Click Start and type Ease in the Start Search box. Open Ease of Access Center
   
2. Choose Use the computer without a mouse or keyboard.
   
3. Check or uncheck the box for Use On-Screen Keyboard. Click Save when you are finished.
   

Now the On-Screen Keyboard should be disabled and not appear.

Source: ITsVISTA Tip 60: Hide a persistant on-screen keyboard in Vista

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