Having more details from you about the actual camera/camcorder (brand and model #) would help in answering your Question.
The problem with just copying from the original SD Card to a USB stick, is that your friend might not have copied the original file & folder structure, or even the correct files. (SD Card camcorders often store "index" and "thumbnail" files, along with the video files.)
Also, without knowing what camera was used, we don't know the file type (.MOV, AVCHD, H.264, .MP4, etc.) that the camera used. Your version of iMovie might not edit the file type directly without transcoding (conversion).
Plus, knowing what version of iMovie you have is also a key detail! Newer versions of iMovie can handle more/different file types than older ones. Tell us what version of Mac OSX you have (either by version number -- 10.4, 10.5, etc., or by animal name -- Tiger, Snow Leopard, etc.) and we'll have a better clue as to which iMovie version you are trying to use.
There are free video transcoding tools for Mac, like HandBrake, that will allow your iMovie to import and edit other video formats: see http://www.handbrake.fr
And upgrading your Apple QuickTime to QuickTime Pro (for $29 on Apple's website) will allow you to handle more video file types directly on your Mac.
And since this is for an Advanced Placement class project, make use of your school's Library or Media resources & staff. There are teachers and school staff whose job it is to help you figure out these kinds of technical issues, so that you succeed in your projects & homework. Budget some project time to politely ask for help, and you may find a school editing workstation available to solve your video problem.
You've never used the Y!A "Additional Details" link to update a Question before, so just go to the Action Bar below your Question, and mouse-over the "pencil icon" Edit menu. Then give us more details about the camera and your software, for us to give you better help & tips.
hope this helps,