windows filename structure

I am trying to copy/merge files from an external harddrive onto my c:drive

I am getting the option quite frequently (too often to work around manually), standard windows screen to resolve duplicate filename conflict- ie. copy and replace; don't copy; or copy but keep both files.

my problem/query is that the filenames are not the same...eg. "EXTRAC~2.XLS" trying to overwrite "Extractps.xls". by appearance (and even checking file properties) those filenames are strictly very different.

I tried to research, and suspect it has something to do with filename structures (I am running windows 7 home premium x64), but cannot get succinct confirmation/explanation of this nor the simplest course of action to resolve- ie. is my system somehow 'shadowing' the long filename in a way that I cannot see, and which could be defaulted as the 8.3 filename that otherwise appears totally different in windows explorer? I had read this is a possibility to maintain backwards compatibility, but do I need this turned-on, and if not how to turn-off?
or, is there something else at play?

thanks
-pson


just to add...I'm also having a funny, probably related problem.
the file referred above "EXTRAC~2.XLS", as a workaround I had changed it to "EXTRAC~2zzz.xls" in order to copy it manually. however, I cannot now change the original filename back to "EXTRAC~2.XLS" in the original folder where it is the only file in that folder (so there could not be any conflicts/duplicate)...I'll take someone's help to explain/resolve all of this headache by windows.