iTunesFixer is a tool to repair the nasty iTunes 4.9 Bug where iTunes recognizes music files as quicktime movies. Many people have this problem. You may read more about that here:
This tool does exactly what's explained at MacFixIt: It changes the creator code to 'hook' (that's the code for iTunes) and the type code to 'MPG3' for .mp3, 'M4A ' for .m4a and 'M4P ' for .m4p files. No other files will be changed than these three extensions.
Just drop some files and/or folders on it (or your complete music folder) and it will repair the type and creator codes of your files. After repairing your files there should be no problems with cover art and iPod transfer anymore. Any questions, email the author