finding duplicate files in backups

[Abhishek Dixit]

Hi,
I have a 1 TB USB used as backup drive. Due to various reasons same
file existed in different file systems and has been backed up multiple
times in this 1 TB hard disk.
I want to keep only one single copy of those files.The problem is
these files are spread in different file systems and (multiple
partitions) and are present here and there at various locations which
I do not remember.
I want to achieve following

1) Reduce n number of occurrence of same file at different location to
1 occurrence.

2) Since I do not know the name of files which have multiple
occurrences how can I easily find this.

3) Is there a way I can create an index of files and directories
present on my laptop for example when you open a book then each book
has an index page which tells on which page number what is present.The
same way.

What can be an easy way to achieve above?
-- 
Regards
Abhi