if you tell us how big you need them it should be fine. If you tell us what style(realistic, cartoon, etc) you want it should be really fine. And I don't really think you will put 3 years of work because the world ends in 2012 Joking. Just give us more info
There are lots of ways to make a trailer.
•Use Adobe Flash animation options
•Make images with textboxes at the bottom
•Easytoon is really good(but you have to color them in GM editor)
•The most stupid thing I can ever say: Download pivot 3 beta and use its BMP importing options
•Create effects with PS and ImageReady.
•Record real people, convert the video to GIF and then use photoshop's options to cut background and place your
and other and other...