Get an external DVD burner, unless you know you're going to be using it all the time (like on a daily basis on the road.)
The 12" iBook would be an awesome computer for you. Hook up an external DVD writer (the components can be put together for probably under $50, and you don't have to be technically inclined to be able to build one yourself.) and you're all set.
Don't forget about Apple's education discounts either. Since you're a teacher they offer sometimes up to $200 off their products...although for the iBooks it's between $50 and $100 off. But every little bit helps, right?
