Is there a hardware cost for x86 to x64 translation on a processor?

Does anyone know if there’s a hardware/processor level cost in converting x86 to x64 instructions on the processor? I ask because I heard that 64bit compiled programs work better than 32bit programs in 64bit vista/windows 7 and wasn’t sure why this would be an issue and if it was and issue if it was hardware level or something at the windows level.