It sounds as if you are being very practical by taking pre-engineering coursework and also following your heart. If you have web construction skills and can self-teach adobe photoshop or dreamweaver, or use a simpler program that is freely available on the web to create a web page, then construct a webpage incorporating a video, audio and/or powerpoint slides. The main purpose of your portfolio is to deliver a strong, clear message. If you create the project on your computer, then create a disc with the completed project to include in your resume.
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Regardless of whether your portfolio project is delivered in electronic or print format use a spell check and grammer check program and proof read your message to be sure it is clear and easy to read. Perhaps one or more of your teachers will help you proof read the content. If you are in the Bridge program, then you may have access to resources at the university libraries.
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Also, if you can get feedback on your presentation from senior graphic design students -- in advance of your interview, they can tell you what the admittance board is seeking, and what to accentuate. Best of luck!