If you want to play it safe, do not assume that the user's personal folder is on the C drive.

The windows registry (at least on my computer) contains the personal folder for the user

HKEY_CURRENT_USER\
  software\
    microsoft\
      windows\
        CurrentVersion\
          Explorer\
             Shell Folders\
                Personal\
[download]

I suppose that there is a CPAN module that should be able to read the Windows registry.

update

http://search.cpan.org/~adamk/Win32-TieRegistry-0.25/TieRegistry.pm