Webcams and iMovie?

Hi, I just received a new Gateway laptop, and I was surfing through YouTube one night and saw some cool effects being done with a cam and a program. The guy said he used iMovie. Is there any way I can open the iMovie through my Vista laptop? It's a .dmg file, and I tried downloading the trial version, but windows can't open it. I'm not even sure if this is the right place, but I'm just trying to find out an answer. Any help is, as normal, very appreciated. Thanks.