Files/Folders open w/ a DOS window

In my WinXP Home O.S., I have no idea how I did it, but my desktop icons, when opened with the left mouse click, open a DOS prompt window with the target line, instead of the expected graphic interface. I can't figure out how to return the preferences of the interface back to the standard opening of folders and files in the windows GUI. I actually have to right click and go down to the open command in the drop menu. Also, the drop-down menu has a new choice at the top, in bold letters "Open Command Window Here".