Update:
Version 2 is now available, you don't need USP10.DLL. It's included (XP).
Download in our mirror here http://www.khmerchristian.com/download_resources/ Just search by typing "Unicode".
Install it, restard your computer and it's done.
----------------------------------------- Old message ------
http://www.khmeros.info
Instructions can be found at that site. However, I found that more info is needed; or it maybe just me that I didn't dig enough in reading. So I write some basic recomendations here. It might be helpful to you:
(For Window XP) When you install, the installer will ask for file USP10.DLL. This file is part of the Window's complex Script, to enable the keyboard to be able to write in Khmer. It can be downloaded here http://www.dlldump.com/download-dll-files_new.php/dllfiles/U/USP10.DLL/1.0420.2600.2180/download.html
Donwload it first.
After you have installed, be awared of the changes in your typing. You should see the language selection for typing in the left side of your window bottom bar--EN=English & CA=Catalan. The complex script for Khmer unicode is fall under Catalan. Just toggle between to the two, to type English or Khmer.
The Kheyboard icon should also be shown next to it. If you are using "Khek brother font" you could toggle between English (United States) and US-Khmer (KheK). If you don't see the Keyboard icon, you could enable your keyboard icon in the control panel of your window. (If you need help just send me the message at siteadmin ).
For Mac User, you need to read at the Khmer Os info. I don't have one. If the Lord's willing I'll get MacAir.....lol 
... Just "Air" for now. http://www.apple.com/
