I want to know if there is a difference in the magnification of a Canon PowerShot S3IS and a zoom lens for Canon EOS 30D.

I’m thinking of buying the Canon EOS 30D but don’t know what lenses I should buy with it. My interest is in nature photography (mountains, beach, wildlife) but have never invested in a good camera. I don’t know a whole lot about specifications for different lenses and need some good recommendations for starting photography as a hobby.