There are plenty of people more expert that I when it comes to DME, but I'll give it a shot.
Yes, call Disney Travel to make DME reservations and give them your flight information. A few weeks before your travel dates you should receive a package include a voucher for the DME transfer and special luggage tags.
I'll assume you want DME to handle your luggage for you and deliver it to your resort. If so, put the tags on before you check your bags at your departure location and you won't see your luggage again until about three hours after you get to WDW, when it will be delivered to your room for you.
When you arrive at MCO, AirTran comes in at Terminal A and DME is in Terminal B. That means you'll have to take the little train from the gate area, then cross the central part of the airport to the Terminal B side. The DME welcome desk is on level 1, so you will need to go down two levels via elevator, escalators or stairs AFTER you get to the B side.
At the DME desk, they will check your vouchers and direct you to some cast members who will show you the line for the bus to your resort. If you have larger carry-on items or don't want to mess with your carry-ons, they will put them under the bus for you. Otherwise, just board the bus and get ready to go.
Your bus will take you to your resort and may stop at as many 2-3 other WDW resorts before dropping you off. All-told, a typical time span from when you get off of the plane until you get to your resort is about 90 minutes. After that, check in to your resort as normal and go do what you want to do. Your luggage will be delivered to your room, but you don't need to be there when it is. Tips for the bell staff are included in the DME service.
On your return, you can use the RAC service to get your boarding passes and check your bags at your resort. If you want to check your bags, you need to do so no sooner than 12 hours before your flight and no later than 3 hours before your flight. The RAC desk is open from 5:00 a.m. to 1:00 p.m., so some flight schedules won't work for the service. If you have carry-ons and plan to head to the parks, DTD, etc. on your departure day, those items can be checked with bell services and picked up before you have to meet your DME bus.
DME will schedule your pick up at your resort approximately 3 hours in advance of your flight departure time. You should get information about the time in a package left on your door the day before your departure.
You need to be at the bus loading point about 15 minutes ahead of your scheduled time, so be sure to be back to your resort in time to collect your bags and take care of anything else you need to.
That sounds like a lot, but it's really easy and a great service!