I have just started Disney Character Training for my 2 1/2 year old DS - he, too, is a Barney fan. Our trip is tenatively scheduled for September 2004 and I think he'll enjoy things more if he at least recognizes the characters.
I tried to get him to watch some of the movies, but about 20 minutes into Cinderella (my favorite!) he says, "doesn't anything HAPPEN in this show?" Okay, so he's not into Princesses, but he does like Toy Story and Monsters, Inc. - so I have hope for him that he inherited the Disney gene.
I have started buying him the Disney Read-Aloud Storybooks. They are about $9 each retail, but I just got Lilo and Stitch 1/2 off at the
Disney Store this week! There are a LOT of words in these books, so I mostly paraphrase what is happening on each page. These are beautiful hardcover books that I'm sure we will enjoy for years to come. Also, I just checked
Amazon and found a collection of stories for about $11 called "Disney Storybook Collection."
As for Mickey and Minnie, I found a great book called "Mickey Mouse Stories" at Ollies Bargain Outlet which DS just LOVES! Check the Bargain Book section at your local bookstore. Amazon shows a lot of Mickey books that are out of print, but many sellers in the Marketplace are offering them for not too much money.
We introduced DS to Mickey by getting him a Mickey Mouse plush for Christmas last year. He had never seen a Mickey video or book at the time - we just told him it was Mickey Mouse and now he can recognize Mickey ANYWHERE!
I think that toddlers will be less apprehensive and have more fun if they are familar with the characters in advance - but if they don't have Disney Boot Camp like my little Nate, I'm sure they'll catch on VERY QUICKLY while at the parks.