Hi Angi!
You can get more information on various Military Discounts
here. That particular page currently just shows discounts until the end of September, but Disney recently announced that the discounts will be extended into 2012. Here's a
link to the announcement on the Disney Parks Blog. By the way, thank you to you and your husband for defending out nation.
With regards to the weather, I've been to Walt Disney World many times in October. The weather is generally warm and can even be hot during the day. At the same time, it can be relatively cool at night requiring a light jacket or sweat shirt depending on what you are used to. However, I don't think I've personally ever used a jacket in October. The high is typically around 81 degrees F during the day and 65 degrees F at night.
By the way, be sure to look into Mickey's Not So Scary Halloween Party. It's a lot of fun and I've never met anybody who didn't enjoy trick or treating in the Magic Kingdom!
Enjoy planning and write back if you have any more questions.