You don't have to be ultra creative to teach preschool, you do however need to know how to make use of resources. The Internet is filled with resources that will help make your job as a teacher easier.
Some of my favorite websites for preschool crafts, activities, and song lyrics are: Kid Zone, DLTK Kids, and Kididdles for music.
As for classes that you could take, there are a number of them. There are basic early childhood education classes taught by colleges, but they do not really teach creativity.
One of my favorite places to learn creativity is Lakeshore Learning Centers. It's a store that sells teaching materials, classroom materials, etc. They offer free teaching workshops which are fantastic. The workshops generally have a theme, and they teach you everything from songs to crafts, games, and more. You usually get a certificate at the end, and some colleges will count their free workshops as part of your instructional hours. The classes are an hour long, and they even have giveaways where you can win supplies for your classroom. You can learn more about their workshops at:
One of the best ways to learn hands down is to sit in on other teacher's classrooms. Talk to other teachers, let a parent helper take a day off, and enjoy seeing how another teacher runs their classroom.
Honestly, a lot of the ideas that I used in my classroom came from children's television programs like Barney the Dinosaur. I actually can't draw worth a lick but I learned the basics from a children's television program called Pappyland.
The key to creativity is to find what you are good at and go with it. Some people love to sing, play a musical instrument, and write song lyrics...I can't carry a tune in a bucket. But the thing about preschoolers is they don't care if you sing out of tune. If music isn't your thing maybe art is and you can show kids how to draw, paint, sketch, and so forth. There is also writing, playing with toys like LEGO, making up stories, playing with puppets, make believe, and so many other things. Find what you love to do and incorporate it into your classroom...that will go farther than all the training in the world.