You trim a clip by placing it on the timeline and dragging the ends in so that you're removing the parts you don't want. (You can, of course, also use the slice tool to remove stuff from the middle.)
You're correct that this will not affect your original footage (which is a good thing). But you can output this video by going to Share/Personal Computer/DV-AVI. This will produce a trimmed clip that is virtually identical in quality to the original. Then, if you'd like, you can even delete the original.
I have two suggestions, but someone might have a better one.
I think the best solution is to reduce the WorkArea Bar to only extend over the portion(s) of the clip you want to keep and under the Share menu I suggest using the PC option and export as a DV AVI and check the option Share the WorkArea Bar Only. You will need to move the WorkArea Bar around in your clip if you have more than one section you would like to keep. I have found using the split clip (ctrl +K) a good way to mark in and out points on the timeline to move the WorkArea Bar to (there is a black vertical line generated when the two line up). Minimizing the work area with the slider moved all the way negative is a fast way to move the ends of the WorkArea Bar to your splits - then expand to make sure the WorkArea Bar is at the correct point.
Second option - If you used a minidv camcorder for example to make the clip - When you view your 24GB clip note the in and out times you would like to keep. Then only recapture those sections and delete the 24GB.
Each of those methods will work very well.
If one is going to use the WAB, or Steve's manually setting the In and Out Points, and possibly the Scissors/Razor, and then Share/Export, that they not edit too closely - leave about 30 extra Frames of material. These can be edited out, when the Exported DV-AVI is brought into a new Project, but they can also be used as the Handles for any Transitions. If one cuts too tightly, they will not have those Handles, and will then be loosing some of that edited footage to Transitions.
I'd also suggest that one does NOT add any Transitions in the Project that will be Exported, unless they are 100% certain that those Transitions will stay and not need to be altered in any way, when the footage is Imported into the new Project.
Too often folk will edit too closely, and then be confronted with no Handles, or needing to change out a Transition and not be pleased at the answer on how to do it.
Just something to think about of later - no surprises that way, and at the worst, you just Trim out a few dozen Frames.
Thank you for all the suggestions. Unfortunately, I can't figure out how to get the AVI settings to accept more than 720x480, even in the advanced options, and this is considerably lower than the 1920x1080 that the original video is recorded in. I must be missing something obvious.
Perhaps one of the H.264 options, which does have some 1920x1080 options would work as well?
You are correct that .avi option is not HD. I hope to start making Blu-Ray projects this fall, but I usually shoot in HD. My camera is minidv so I save under MPEG2 1920X1080i 30 option.
You are correct. The AVI Presets are basically for DVD-Video (SD), or similar.
You will need to choose one of the HD Presets, that matches your source footage.