Merging this .reg file into Windows 7 or later will enable the hexadecimal Unicode input method. After importing this file into the registry, you will need to log off or reboot before input method works. The download file is very simple, consisting of:

Windows Registry Editor Version 5.00

[HKEY_CURRENT_USER\Control Panel\Input Method]

Once enabled, arbitrary Unicode characters may be entered into most Windows applications (subject to an appropriate font being installed on the computer) by holding down Alt and pressing the + key on the numeric keypad, followed by the USV in hexadecimal (using the main letter keys and any of the number keys).

Unfortunately this input method does not work reliably in some applications, including Microsoft Word. However, Word does support the Alt-X method of input.

These input methods are described in various places including  this article on Wikipedia.