Already posted a (hopefully) somewhat helpful reply on Sandee's topic page. I am the same-new at computer's and probably can't get any pictures up.
My Mom is our real costume-aholic!
Her horse has been a High School letterman (football) and she a cheerleader; Medival maiden and knight's horse and a Medival knight and horse (she like the "lady" better); Alice and the white rabbit in his Queen of Hearts get-up (the horse is black; so yes, he was covered almost comletely up-only ears, very tip of muzzle and hooves showed); Bo-Peep and her sheep (same scenerio for horse); 50's Poodle-skirted teen and the horse was "Elvis" in his white jeweled outfit; Betsy Ross with "yankee Doodle" (a dressed up stuffed monkey toy) on his "Macaroni" patriotic 'pony'; there's probably more! That poor horse has been covered in fleece and fake fur from nose tip to tail tip in 90 degree weather more than once.
(we do dress him at the very last minute) He is so tolerant to these costumes when he is not always the most tolerant horse on the place. But the last time we went to dress him in his sheep outfit on a 90 degree show day he pinned his ears at me!
Boy did I feel like torture-er! He still let me put it on and was tolerant through the (mercifully) short class. We use Suitability's mini blanket/sheet and/or hood patterns for alot of the horse's base costumes. We just adapt and revamp. Like my sister says: remember, it's a costume-the sewing doesn't have to be that good. you're not wearing it everyday!