For Windows: Instructions on how to configure Google IME to honor
Harvard-Kyoto among other IME schemes is documented here:
http://daivajnanam.blogspot.com/p/typing-sanskrit.htmlFor Mac: Download and install
LipikaIME. It has built-in support for Harvard-Kyoto.
The important thing to note is that the above solution will let you type Devanagari directly into any Unicode aware software (including your browser) and you don't have to be online to do so. Additionally since you use the same scheme for both platforms, you can switch between Windows and Mac and still retain the same key strokes. In both the above solutions, you can also edit the IME scheme and fine tune it to your personal preferences.
If you are so inclined, you may also use any of the other popular devanagari IME schemes:
Baraha,
ITRANS,
Harvard-Kyoto or mix and match to produce your own like
Barahavat.