Teach me how to create amazing artworks using Adobe Illustrator CS3!!!

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I'll have to do a poster based on Global Warming for my final assignment in University. I'd already finish the outline of my design, now what I want is to make it look realistic. One of my subject is Polar Bear, I want to make it looks like 3D and real, can any one please teach me how to do that??? And recommend me to any website if you know any??? P.S.: Please help me before next Wednesday come... thanks...