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 'http://thesource.ofallevil.com/......' 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.