DSOrganize should come with a folder called "DSOrganize" that you should place on the root of your card. I personally place the DSOrganize.nds file on the root of my card as well, though I'm not sure if this is needed.
Sounds like you either forgot to copy the folder over or you copied it to a location other than the root of the card.
Also note that to boot homebrew, you will need to patch the exec_stub.bin file (in the Resources folder) with the correct DLDI patch. First try the original Supercard Lite file from the DLDI homepage, but if that one fails (be sure to test with several homebrew games) then try the SCSD_moon.dldi file, which is described more at http://wiki.pocketheaven.com/DLDI