Typing aids for MAC:

Unzip, & put them in Keyboard layouts folder, and hold the "OPTION" key for adding the diacritic.

Typing aids for PC:

Unzip, run the program, and choose your default key for adding the diacritic.

A great PC program to type in Devanagari from Latin keyboard is AksharaPad. You can download it from their own website here:

http://kevincarmody.com/software/aksharapad.html