Here is a complete tutorial with source files that do exactly what you want,
multi images upload and delete with ajax, multiple post types and more.

http://www.deluxeblogtips.com/2010/05/howto-meta-box-wordpress.html

Here is a complete tutorial with source files that do exactly what you want,
You can upload multi images by cloning the input field and also you can preview, delete images with ajax, add multi metaboxes to multiple/different post types and more.

http://www.deluxeblogtips.com/2010/05/howto-meta-box-wordpress.html