What you can do is, two ways of getting round this, but no quick solution.
1. Create a smartplaylist with a filter condition that has 'Date Added' and make the date a week or so before you imported all your music.
Now go into this playlist and go to View>Show Duplicates. When you have done this, click on the album column header to sort everything by album.
Now you can sift through all the duplicates and mark them for deletion (I use the comment column for this purpose), then once done go to the library and hunt down the marked tracks and delete them.
Repeat this process until you are happy that all the duplicates are gone.
2. You can use this little app,
Find Duplicates, to find the duplicates on the HD, delete them and then reload your library once it's complete