IF you wnat to type in Unicode Tamil
here is a program that I suggest
http://akelpad.sourceforge.net/en/index.php
Akelpad Portable Notepad in which you can write in Unicode Tamil
All you need is keyman from your portable USB
Let it run in the background. Install keyman unicode kmx
or you can use NHM Writer and select the keyboard layout you like
Now you are set
Run Aklepad
Select options-settings-general tab-default code page UTF 8
view-fonts-latha-12
view wrapwords (control U)
தமிழில் எழுதலாம்
Save it as ave as Unicode
That is all to it
Enjoy typing in a portable UNicode Tamil text editor
Ram