You can send the letter through e-mail copying the text of the proposed letter and placing it with «paste» in the electronic contact form which you can find in the following link:
http://www.primeminister.gr/index.php?option=com_facileforms&Itemid=104

You can also send the letter by mail to the following address:

To the Prime Minister K KARAMANLIS
Maximos Mansion
19 Irodou Attikou St.
106-74
Athens Greece