The %ProgramFiles% registry value that a 32-bit application is writes is automatically changed to %ProgramFiles(x86)% on a computer that is running a 64-bit version of Windows Vista
When a 32-bit application is writing the %ProgramFiles% registry value on a computer that is running a 64-bit version of Windows Vista, Windows Vista automatically changes this string to %ProgramFiles(x86)%. This behavior cannot be changed.
This behavior also occurs in the 64-bit versions of Windows Server 2003 and of Windows XP.
For more information on this issue, including potential causes, workarounds, and resolutions, see: Microsoft KB Article KB950407.