I am sorry to hear that mate.. dogs really are mans best friend, and it really is like loosing part of the family when you have to put them down.. It's so unfortunate that pets have such short lives, but i gotta tell ya - I don't think there is any better life than being a dog.
It's funny, they spend their entire lives relying on us for their every need but in the end, its them who gave us more than we could ever repay. My thoughts are with you!
Chris.