There are two software options for video editing in the Undergraduate Library: iMovie and Final Cut Express.
iMovie is considered easier to use but Final Cut Express is more powerful. There is a nice article on Macworld.com about the differences between the two: http://www.macworld.com/article/146782/2010/04/fcevsimovie.html
Apple has created a series of video tutorials about using iMovie that can be found here: http://www.apple.com/findouthow/movies/
eHow.com also has a great step by step guide as well: http://www.ehow.com/how_4838996_use-imovie-apple.html
Final Cut Express
Apple has created tutorials for using Final Cut Express that can be found here: http://www.apple.com/support/finalcutexpress/