Hi Eli,
First, thank you for your service to our country. I'm not sure how much you are use to walking around each day but I can tell you that the parks at WDW are big & require a lot of walking & stamina. It may be more comfortable for you to rent a wheelchair even if you don't usually use one on a day-to-day basis.
As of 1-28-10, the rental fee is $12.00 per day in the theme parks (always subject to change). Keep in mind that a rented wheelchair must remain in the park that you rented it from. If you plan on park hopping on the same day, you can save your receipt to show at the next park but you run the risk that they will run out of wheelchairs. If you plan on renting for more than one day, consider getting a "length of stay" rental which will save you a little money.
There is a section on the WDW website devoted to guests with disabilities - click
here.
Here's something that you might be interested in. Each day around 5:00 p.m. at the MK, they hold a Flag Retreat (ceremony where they lower the US flag) in Town Square's Municipal Park near City Hall. If you are interested in participating, check with Guest Relations at City Hall when you enter the MK.
One other quick thing (I know this is way more info than you asked for), WDW currently has some special offers for active & retired members of the US Armed Forces - click
here to see the details for eligibility.
Have an awesome trip!