Hi raysundar,
If you want to directly key in tamil fonts without involving c and p you have to get the software installed. For getting the software please click on this link
www.azhagi.com . Then be guided by the instructions there to download the sw to your device.
Once you have installed azhagi in your computer the rest of the task is easy.
Whichever page you are in you have to just click on the azhagi ikon in your task bar and then click alt and 3 on your key board. This combination of keys act as the toggle for switching between Tamil and English alternatively any number of times. Then if you have chosen the phonetic key board option in the software you have to just key in the tamil words phonetically with English alphabets. What appears on screen will be the equivalent tamil letters. It is as simple as that. When you want to switch back to English just click alt and 3. The advantages of this sw are:
1. you can download a simpler version to your thumb drive and thus it becomes portable between computers.
2. The font is in unicode format and hence is portable freely across internet and there is no need to send the sw across along with your communication for the receiver to decode it at his end.
3. A version of this azhagi is available for cell phone devices too though I have not tried that.
4. as you use the sw you will get familiar with how to get, say, a ந instead of ன or ண though the sw intuitively suggests the appropriate letter depending on the context.
5. If you are a language enthusiast , with the same sw you can toggle between other indic languages too.
Before closing, a word about the man who authored this sw. His name is Viswanathan, a physically challenged young man who studied in an Engineering College in kerala. He has made this available free of cost to any one interested. A great service indeed.
Try it and enjoy. all the best.
out:
Google!! 
