No need to print your boarding passes; all you need to do is check in. You can print your boarding passes when you arrive at the airport.
Guest Relations or Lobby Concierge at any WDW resort or theme park will check you in for your SWA flight. You will need your SWA confirmation number, and you may be asked for ID.
Another way to check in is to use any web-enabled cell phone to visit mobile.southwest.com. This is the method I use; I've been on Verizon for years and gotten excellent signal all over WDW (outdoors, that is - cells don't work well in most attractions, and don't work at all in many - thankfully!) I also know many people on AT&T, and they also get excellent signal all over WDW. Which is a good thing, because I bought myself an iPhone just last night!
When you arrive at the airport, you can print your boarding pass when you check your luggage, or if you don't have any luggage to check, there are free-standing kiosks where you can print your boarding pass. Printing your boarding pass at the airport will NOT alter your boarding group or number - the boarding group and number is assigned when you check in for your flight and does not change if you print your passes at a later time.
