Crawlers/Bots to Automatically Download Files

I need an experienced developer that has lots of experience writing Visual [login to view URL] applications that can crawl the web so as to download various files. 1. Windows applications that can be minimized to the taskbar so as to run behind the scenes. 2. Automatically crawls specified website and downloads audio & video files within the timeframe specified. (NOTE: must be able to do the same thing for a total of 5 different websites). 3. Must be able to download files to a specified directory and in a specified format. 4. Application must be able to verify whether a particular file has been downloaded or not - so as to prevent the same file from being downloaded multiple times. 5. Must be able to control how much bandwidth it is using so as to not impact the computer's performance too much. Experienced developers only... please be sure to verify your experience if at all possible. Thanks...