Custom Downloader

I need a custom app to download files from a webserver. Similar to what is generated by GetRightToGo (look it up.) Features: Multiple threads for faster downloads Compare MD5 hash of each file to ensure correct download Can be paused, exited, resumed at any time Multiple download servers (minimum 1) The executable can be built on the fly from a web server with custom list of files to download Downloader requests username & password, which is used to login to a session in order to download the files (the app must post the username & password to a login page, which will return a session cookie, without which the files will not download.) Small footprint I preferably want this for both Windows XP/7 AND Mac OS X (Intel). If you can make it for both then you have an advantage, if for only one then please still bid and I may still accept your bid. Please complete within 1 week. Please post what language you will use to develop the application.