Thanks to all of you. I am really grateful for your suggestions regarding this somewhat uncommon problem of mine.
@NiLuJe: You're quite right. Bengali uses multi-glyph ligatures. They don't have different unicode representation. It's the job of the rendering engine to render them properly.
For all its worth, I mailed amazon.com customer care requesting this feature in the next firmware upgrade. But I'm not really hopeful though. Can any of you tell me if any of the reading apps running on top of the Kindle OS support complex script rendering?
@tomsem: I am currently following what you suggested. I'm generating pdf's from xelatex and it works quite well. For anybody interested in doing the same, I'd share the method I followed:
http://methopath.wordpress.com/2008/...gali-in-latex/.