I was having a lot of problems with the standard WordPress Import plugin and have been looking for alternatives. The Media Tools plugin does an excellent job of importing images into the media library.
Thanks very much,
P.S. If the standard WordPress import tool doesn't work, I found that you can import pages, posts, and comments from WordPress.com using the WordPress.com Importer plugin:
It won't import images, but Media Tools will. The combination of WordPress.com Importer and Media Tools works very well.