Among the various annoying aspects of running x64 versions of Windows (XP or Vista) is that the registry is split into two sections: x64 and x86. When 64 bit applications access the registry they do so directly, as you would expect. However if a 32 bit application access the registry it is mapped into a special 32 bit section.

Scripts that interact directly with the registry may yield unexpected results if you are running a 32 bit version of PERL.EXE on a 64 bit version of the operating system. More details can be found in Microsoft’s KB article 896459: http://support.microsoft.com/kb/896459