The Council On Foreign Relations claimed that it has obtained a copy of the letter from Iranian President Mahmoud Ahmadinejad to US President George W. Bush.
The link here points to a pdf file. It is not the official translation. I have to say that the quality of the translation is not very good. It is kind of crude and punctuations marks were not used properly. But the central points of the letter did come through.
Have a read and draw your own conclusions, instead of just getting the sound bite version from the mainstream news outlets. Most of them just quoted one sentence from the letter, namely, the one when he commented about rights of technical research.