I sympathize, seaside, cuz I was Diet Pepsi addict for years. I would drink at least 64 ounces of diet soda a day! I hate to burst your bubble, but diet coke isn't acceptable as an alternative to water because it contains so much caffeine, which causes stalls for many people and is just plain awful for you; I suppose a caffeine-free soda would be better, but still not ideal. Crystal Light is okay if you just can't stand the taste of water, and many people here drink it and use the mix. But the important thing is to try and get yourself into a life-long habit of drinking healthy fluids.... so you realllly oughtta try to drink more plain water.
Why don't you start slowly? Have 20 ounces of water, 60 ounces of Crystal Light, and a diet coke or 2 as a "treat"? I and a few others here still drink diet soda but we limit them to a couple a day as "special" drinks-- gives us something to look forward to. Gradually increase the water so you're drinking more and more plain water every day. It will feel like you're drinking a lot, but that's okay-- you *do* need to drink a lot, probably more than you have on any other plan. But don't worry; we'll throw you a branch if you start floating away!