Not sure without installing other software. but glary utilities is a great little free program that cleans registrys, etc and there is a built in applet to remove duplicate files. I know there is also a few nice freeware programs available at the pcworld.com website under the downloads sections and then under utilities. Think it is called digital volcano but I am not 100% sure.

Hope this helps

If you decide you'd like to try some software to do this, FSlint works pretty well. It is for Linux, but you might have some success running it through Cygwin.

http://www.pixelbeat.org/fslint/