Find all files in a folder

I am looking to create a program that finds all files of a certain type on my desktop and places them into specific folders, for example, I would have all files with .txt into the Text folder.

Any ideas what the best way would be to accomplish this? Thanks.

I have tried this:

string startPath = @"%userprofile%/Desktop";
string[] oDirectories = Directory.GetDirectories(startPath, "");
Console.WriteLine(oDirectories.Length.ToString());

foreach (string oCurrent in oDirectories)
    Console.WriteLine(oCurrent);

Console.ReadLine();

It was not successful in finding all of the files.