I take both ECA (and a cup or two of coffee on top of that) and I take creatine. I have had the benefits of both with no problems. The main conflict bw caffeine and creatine is that creatine helps your muscles store water (with creatine/glycogen etc), and caffeine is a diuretic. If you drink plenty of water- which you should be doing anyway- you should have no problems. ALTHOUGH! I recommend not starting caffeine if you don't already. It is not a good habit. I am an addict, decided not to bother quitting until my body fat gets low enough. If you don't take caffeine yet- don't start, getting enough sleep will keep you from being tired, and creatine will help lift those heavy weights!
While you are off creatine, caffiene shouldn't matter in the slightest, when you are back on- still shouldn't matter if you drink enough water. If you are only drinking occasional sodas, certainly doesn't matter at all either way.