I think that you also need to cover the old kill first ask questions 2nd mentality that many people have for snakes.

I do several presentations a year to elementary schools and preschool aged kids and you be surpized how many kids only experience with snakes is seeing mom or dad killing snakes with a hoe or shovel.

I normally talk about the positive things that snakes do like eating rodents. I also mention that the presence of reptile and amphibians in an ecosystem is a way to see if everything is balance and healthy. Both types of animals seem to be effected early on if something is up with the environment, I am sure you could find some research about biological indicators.

I am surpruzed that your college will not let you bring in the snake for the presentation. Have you checked with the biology department? Many have reptile collections and they might let you use one of their snakes for your speach (I bet the real reason is some snake phobic english prof, one who really needs to listen to your speach)

Good luck