Replying to Adding Effects?

Hey NS, I'm a pretty big noob when it comes to serious editing. I've made some ski edits with my friends before but that's pretty much it. So for our Spanish final this year the assignment is to make a movie all in Spanish. We have a couple scenes that could use some special effects like explosions, etc.

I use Vegas Studio HD 10. Are there programs I could DL that would allow me to add some effects?

+k for all good answers of course