You want to use the Media Manager. It allows you to copy just the clips in your sequence into a new project. Once you verify the trimmed sequence you can delete the media from the original project. Here is a tutorial.
http://fcproducer.com/2007/11/final-cut-pro-media-manager-tutorial-part-1/
A word of caution, carefully examine the copied/trimmed sequence before you delete the original media. Sometimes using Media Manager can deliver unexpected results, such as missing media.
Lee Berger
www.leebergermedia.com
