There are 2 possibilities. If you want the files to launch itunes when double clicked the you have to change the type and creator code using the get info function of ResEdit or a similar app like Techtool Lite. Quictime is "mp3" (or mpeg) and "TVOD". itunes is "mp3" and "hook". Do not include the quotation marks. Doing this will also change to the proper icon.
If you just want the file to play in tunes then add it to your itunes library from within itunes... from the file menu choose "add to library".