After some time you will realize that how many copies of the same files you have!
There is no easy solution to find and remove duplicate or similar files with Windows XP. Microsoft does not provide any in build software to do same thing.
However with the a special program called DupKiller you can find find unneeded copies of files in those locations where you even would not consider to search.
From DupKiller web page, “The fastest and the most powerful tool for searching and removing duplicate or similar files on your computer. Complicated algorithms, built in its searching mechanism, perform high results — rapid file search. A lot of options allows to flexibly customize the search.
There is comparison not only by name, last modification date or size. One can compare files by their contents, and what’s more, to set what per cent they must match; one can search different-length files, include or exclude files by mask, etc.
A lot of scan options helps flexibly customize your search.”
You can download a free version here (2.32 MB).