You can check it over here:

You can find that under list "The following is a list of all Support Tools in Service Pack 2:", 'dupfinder.exe' is available.

Alternatively you can download Windows XP Service Pack 2 here(Microsoft site):

I am not sure if the site '' is official Microsoft site or not. But over there you can check that 'dupfinder' is available in Service Pack 2.

This is a link to get a free Duplicate Finder from third party for Windows:

I have used it to find duplicate photos on my system. It is good one.