Crop cuts off part of the image, unless that's what you're looking to do. If you have Mac OS X Leopard, you can use Preview to resize the image. Drag the image to the Desktop or set iPhoto to use an external editor when clicking Edit. Once the image is in Preview, under one of the menus is an option for Image Size. In there you can change the resolution of the image, which preserves the viewable area of the picture unlike cropping. Once done, save the edit on the Desktop. If you already had a copy on the Desktop, just overwrite it. If you set Preview as the external editor, you cannot save the image in the present location because nothing except iPhoto can write inside the library package. Then reimport the image back into iPhoto or do whatever else you want with the resized image.