Also, for anyone confused- Just download the puush that's nine replies or so above this (- P l u e m -'s post), and then rename the corrupt osz that you get to a zip file. (Just change the last bit of the name from .osz to .zip).
Then, like Lekxion said, extract the newly renamed .zip file to your osu! Songs folder (It'll automatically create the beatmap folder for you, you don't need to make one by yourself).
Then, go into that folder, and copy everything except for the .osu files, .osb files, the mp3, the video, and the background image. Put those files (the ones you copied, there should be four- approach circle stuff and a sound effect) somewhere outside of the beatmap folder (for now). When you're done, the files should no longer be in the beatmap folder.
Then open osu! and find the map. It should be there, just fine, working correctly. After you've confirmed that it plays, you can go put those files you moved out of the beatmap folder back in it, and they'll work fine.
For some reason, I couldn't get it to work for me unless I opened the map in osu! with the skinning elements removed at least once, which is why all that stupid copy/paste crap is necessary.