I was recently trying to encode an ogg file, when my computer crashed completely. Not even the mouse was moving. I tried to reinstall the program, when an error came up, saying that the files ogg.dll, oggds.dll, vorbis.dll, and vorbisenc.dll.
Already existed? Were in use?
Try what xhaos recommended and if that doesn't work - see if you can get a copy of knoppix, or some other livecd linux distro, and you can then boot up in linux, mount the windows filesystem, and delete the files from there. This kind of assumes that you aren't tethered to windows though. Good luck.