Any advice on my WW1 RADIO schoolproject?

Hi.
I'm doing this History project at school. It's a group project and we basically have to make a radio show of 5 to 8 minutes on World War 1 .

Stuff we are doing include interviewing a soldier in the frontlines during a battle. There will be a loud explosion and the interview will be cut off "due to technical problems" and go to commericals...hehe

That's just an example. But what i need is SOUND EFFECTS!! Sounds of machine guns, explosions, patriotic background music (for propaganda ads).

We have to use iMovie to do this project.
Problem: I don't know much about Mac computers. Does anyone know stuff about iMovie? Does it use .WAV files? (i don't have the program at home) If it does, i can use gun sounds from Counter Strike!

Can anyone tell me good site(s) where i can easily download the kind of sound clips my project needs?

And u are free to give any suggestions for my project

Thanks