I get rather annoyed with the narrator. Using this as inspiration here is how you do it.

Update: Another solution is available at http://www.hmemcpy.com/blog/2012/12/how-to-disable-windows-narrator-appearing-on-win-enter-in-windows-8/ which uses Image File Execution Options instead.

Note: You can just delete it, but windows will restore it every time an update is installed

• Open C:\Windows\System32
• Open Properties of Narrator.exe, goto Security Tab, Click advanced
  
• Change the owner to yourself
  
• Click ok, and accept the warning
• Now back on the properties, click edit
  
• Add yourself, then explicitly deny Read & execute and Read. Click yes on warning about modifying security on system files
  
• Change owner to SYSTEM
  

Win+Enter now won’t do anything :D