Transliterate an entire document

[sarm...@gmail.com]

HI,
Can you let me know how I can transliterate an entire Tamil document
which is writen in English (meaning Vannakam etc instead of the Tamil
alphabets).
Your Transliteration link http://www.google.com/transliterate/indic/Tamil#
allows me to change only one word at a time. Is there a better way to
transliterate an entire document?
Thanks!
Sarmishta