Knowledgebase

If you want to change the Caps Lock key to a Shift key, use the following registry changes:

Windows Registry Editor Version 5.00

[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Keyboard Layout]
"Scancode Map"=hex:00,00,00,00,00,00,00,00,02,00,00,00,2a,00,3a,00,00,00,00,00

If you want to completely disable the Caps Lock key, use the following registry changes:

Windows Registry Editor Version 5.00

[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Keyboard Layout]
"Scancode Map"=-

After applying the registry change, reboot you’re system for the changes to take effect.

Found at : http://www.howtogeek.com/howto/windows-vista/disable-caps-lock-key-in-windows-vista/