Where do the AIFF files go????!!!

Ok, let me get this straight. You deleted a bunch of duplicate 'songs' and found at least 100 [Audio Interchange File Format|http://en.wikipedia.org/wiki/Audio Interchange_FileFormat] 'songs' in the trash and you wonder how they got there?

Most people would keep them in their Music folder or in their iTunes Library.

If the "Advanced" preference in iTunes is set to copy files to the iTunes library, just drag the folder to the iTunes window and it will copy the files back to its library.

Just trying to fathom your problem here. So you deleted duplicates. Do the songs still play in iTunes? Try highlighting a song and go to file > show in finder and then Get Info and see if it comes up as an aiff file. If so then you probably have your settings set up to import all music files as .aiff . I am presuming that you are expecting to import them as mp3s? If so try
iTunes > Preferences > General > Import Settings > set to MP3 and not aiff

If you need to convert them all. Selsct all songs and then Advanced > Create MP3 Version. Once this has been done (may take some time depending on how many songs you have) then select view by date added and delete all songs before todays date.
I am presuming you want to free up space as .aiff files are much larger than mp3s.
As for the ones from trash, if the song still plays in iTunes then you can safely delete the duplicates that went to trash.

But then again I may have misunderstood what you are aiming at here. In any case make sure you have a backup.
Cheers