I'm about to download Java 8 (Update 51) for the SMARTAC+ GX10/GX20/GP10/GP20/GM10. Should I choose the 32-bit or 64-bit version?

Install the 32-bit version of Java Runtime even if you're using Windows 64-bit (even 64-bit Windows comes standard with Internet Explorer 32-bit). If you install Java Runtime 32-bit and waveforms and other items do not display correctly, you may be running Internet Explorer 64-bit. In that case, uninstall 32-bit Java Runtime and then install 64-bit Java Runtime.