Program x86 is the directory for 32-bit, dude. You'll need to install the 32-bit version of EZD or Superior (whichever you have). I believe the EZXs are independent of bit type, so you don't need to reinstall them.
I don't think Cubase 5 was available as 64-bit. I think that happened on 6 (might be wrong about that, though).