Here is the fully arranged keyboard for Khmer.

I missed 3 of the characters but I think it will be fine. Those three characters are barely used in real life anyway. Mostly used in Pali (Buddhist scripting).

-normal : 29 total
-shift : 29 total
-symbol page1 : 29 total
-symbol page2 : 29 total
-accented : 29 total
-accented+shift : 29 total
3 characters shorts but it will be fine.

Ubuntu 9+ would happily displaying the characters, Windows Vista/7 would display this as well. Windows XP will required khmer Unicode to display these properly in MS word.

http://www.khmeros.info/drupal612/en/download

Windows vista/7 may display in very small due to DaunPenh font type. But if use KhmerOS font it will display perfectly.