The ISO downloader leverages the download functions that are integrated into Windows and .NET. There's no pause and resume function in there by default, and we're not going to implement a new download module from scratch.
If your internet connection is slow or unstable, and you can't grab an image through the downloader without interruption, my suggestion is pasting the links into a download manager.
My personal recommendation: Free Download Manager (http://www.freedownloadmanager.org/)