I've been doing WW since November, 2007, and I've lost 48 pounds. I was at Disney in May, and I was really freaked out about it, but it was fine. I missed a weigh-in while I was at Disney, but when I got back (2 weeks since my last weigh-in), I had lost 1.8. Here's some of what I did:
-I decided that maintaining was fine for me on vacation. You get 4 extra points a day.
-I considered doing core, but decided to stay on flex. but I did feel strongly that I wasn't going to count points while on vacation. So, I focused on not eating too many carbs, and usually choose chicken, seafood, and ate a lot of veggies.
-Whether on vacation or not, my rule is "DON'T GET HUNGRY." That's when I binge. Snack often and snack healthy.
-I didn't refrain from dessert, but I took small portions from buffets, and shared elsewhere.
-Do not underestimate the amount of walking you do at Disney. You can easily do 4+ hours of "leisurely walking" a day. That's a ton of extra points. Plus, you will probably swim, run for a fast pass, etc. Not only does it allow you to eat more, it means you NEED to eat more to have the energy for all of that extra activity.
-Just relax, this week isn't going to make or break your new healthy lifestyle. I won't speak for you, but I know that I didn't get to be 80 pounds overweight because I overate on vacation. My problem is a daily addiction, so dealing with it day in and day out is far more important than the few days you're at Disney.
-My WW leader says that she usually gains 3 pounds on vacation. This was amazing to me, because I realized that that can be ok. Enjoy! Food is art at Disney. It's part of the fun. It's an experience.
The fact that you're thinking about it ahead of time means that you're serious about losing weight and making a plan is your first line of defense. You'll do great.
***Edit: Also, remember that you'll be consuming a lot more salt than normal, so expect your weight to be up a few pounds when you first return, but for this to melt off as you get back to your normal diet. I think I was up 2-3 pounds when we got home Sunday, but by my weigh in on Thursday, I was 1.8 pounds less than when we left for vacation.