Don't go cold turkey!  I was addicted to cola for over 10 years.  I seriousely drank nothing but cola every day...  About two bottles a day.  Once I realised it was a problem I tried several times to go cold turkey off it and had some horrible side effects - sickness, shakes, headaches, runs, irritability, dehydration...  It was awful and made me very sick.  I managed to come off it in the end by slowly weaning myself off it a little bit at a time.
 
Sadly it's left me with awful teeth decay (which has all been fixed now, but I still feel ugly) and kidney problems...
 
I didn't drink the diet stuff though as I got shakey if I tried the diet stuff.  
 
Good luck!  You'll feel much better once you kick to coke!