How does file recovery software work?

I wanted to make some simple file recovery software, where I want to try to recover files which happen to have been deleted by pressing Shift + Delete. I'm working in Windows, can anyone show me any links or documents which can help me to do so programatically? I know C, C++, .NET. Any pointers?

http://www.google.hu/search?q=file+recovery+theory&ie=utf-8&oe=utf-8&aq=t&rls=org.mozilla:en-US:official&client=firefox-a :)

Mainly file recoveries are looking for file headers and/or filenames in the disk as I know, then try to get the whole file by the header information.

This could be a good start: http://geeksaresexy.blogspot.com/2006/02/theory-behind-deleted-files-recovery.html