Tawnya,
I have a 6yo son with Asperger's Syndrome, a form of autism. After a trip that was torture a little over a year ago, I found out about the DIS and got lots of advice here. The trip we took in June was great, we only had one major meltdown out of my son the whole week. That's saying a lot for my DS, he normally has 1-2 major and 4-6 minor meltdowns a day.
The best advice I got from here was the Guest Assistance Card (GAC). It allows the child accommodations based on his needs. My son has difficulty with waiting, so ours was phrased "Please allow this party to utilize the entrance for Guests with disabilities. In case of mainstream access, allow party to use ALTERNATE ENTRANCE. At attractions offering Disney's FASTPASS, please allow Guests to utilize FASTPASS RETURN QUEUE'. (I keep it on the fridge so I can get it for the next trip, I did NOT memorize it, LOL). We got ours in City Hall at MK, but you can get them at Guest Services at all the parks.
Following his lead is the biggest piece of advice I can give. We had to give up the 'commando mode' of traveling. A daily break can help, but we had two 'non park' mornings where we just hung out at the pool (or the whale at ASMo). I think that this was the biggest contributor to the lack of meltdowns.
I have a trip report on MousePlanet that covered all aspects of our trip, but recounts some of the Asperger's related events. If you're interested, just go to
http://www.mouseplanet.com/dtp/trip.rpt/report_files/wdwtr02/reardon-mulhall02jn.htm
Feel free to PM if you have any questions. I'll be happy to help!
Suzanne