you can use http://System.IO for searching in directories and you can load video(ogg format) and images(png) using WWW class in unity. The only thing you should do is pass your file path like this :

var url = "file://c:/fridays.jpg";
function Start () {
     // Start a download of the given URL
    var www : WWW = new WWW (url);

    // Wait for download to complete
    yield www;

    // assign texture
    renderer.material.mainTexture = www.texture; 
}

see WWW class reference in docs

Hi,

For text files I do like this:

private var file : String = ""file://c:/files/file.txt";

var reader : StreamReader = File.OpenText(file);

You need to use file:///c:/.... to let this file protocol work....3 slashes