Hi Jo!
How smart of you to start planning now for your 2011 vacation! I have a son that has very similar issues with food, so I can understand your concerns. For us, the stress of traveling can exacerbate many of his issues, so I always try to make sure that I bring familiar things from home to help him. For our son a particular cup was his main 'comfort item' while eating. We brought 3 of them with us on our trips so we'd always have one available.
I also make sure that we have food on hand that I know he'll eat. We schedule a grocery stop for a nearby store to pick up what we need. You could also pack non-perishable things with you. Luckily, you'll have the benefit of staying in a cabin where you can prep at least some of his meals there for him!
As far as restaurants at Walt Disney World, I've not had an issue with them making accommodations. Between my son's food issues and my food allergy, everyone's always been super helpful.
Here's some information to help you with the transition.
Have a Magical vacation!
Amanda