See my post to you in your other thread.
Is it possible that you're actually taking too much insulin before meals, thus causing lows, thus causing the craving for more food, thus causing the weight gain? This frequently happens when first going on insulin.
The other thing that can cause weight gain is that your blood glucose levels start to become closer to normal and your body can finally utilize the glucose for fuel instead of burning fat. That type of weight gain also happens when first going on insulin, but eventually stabilizes.
I'm not a super huge fan of the Byetta/symlin products because I feel they just complicate matters for those of us on insulin. I've had several friends who are T1's try them, and they had problems judging when to take their insulin, as the medications delay stomach-emptying (to make you feel full longer)...but this complicates the timing of insulin. I count carbs and have an insulin to carb ratio, which works very well for me and with which I can still lose weight as long as I don't pig out too often! <sigh>