Amit, if you are using Microsoft Office XP, it already has speech recognition features which can be used in conjunction with any of the Office programs as well as Internet Explorer.
While there's no support for Indian languages, you can train XP voice recognition to understand other regional accents such as British English, or use a different language altogether such as German, French, or Russian.
In your particular case, you can start Microsoft Word in full-screen mode [similar to WriteRoom] and start dictating whatever things you wish to communicate with your father. The font size may be also increased so that he can read the text on the computer even from a far off distance.
The other accessory that you'll find very useful is a cordless headset-cum-microphone [like Logitech] that will help you narrate text even from a distance.
If you have not purchased Office XP, the other reasonable option would be to either wait for Windows Vista or get Dragon Naturally Speaking 9 [related reading].
Microsoft Windows Vista, which is expected in December, has good support for voice recognition and the feature is included in the price of Vista itself. While I have not tried Vista speech recognition myself, the general view in the blogosphere is that it works reasonably well.
If you have no plans to switch to Vista soon, the best option will be to invest in Dragon NaturallySpeaking 9. It's probably more accurate than Vista speech and requires absolutely no voice training. Dragon has support for English spoken with an Indian accent. The standard edition of Dragon 9 should be sufficient for your needs.
Unfortunately, Nuance (developers of Dragon Speech) won't provide a trial version of their voice recognition software products but you could make a safe decision based on the review of Marc Orchant or David Pogue.