|That's a hell of a project.
You'll need to attempt to parse files as specific file types and make sure that they can be read. That means you'll need the spec or a fast execution environment for each and every file type on the system.
If you generally have a lot of one sort of file (say, .pdf) you can speed your search up by making a script that verifies that it can open each with itextsharp, for instance.
"There are three kinds of lies: lies, damned lies and statistics."
- Benjamin Disraeli