um - the last time I used windows you had to double-click to open... Any such hack would eliminate your ability to edit the name of a file, move it or otherwise do anything that requires selecting the folder or file....
That said, if you use column view, a single click will show you the contents of a folder (though it wont launch an app/document).
Also, you may want to look into dock replacements (or just use the dock itself) that create buttons (like the old button view in OS 9)