someone wants to know why you cannot run a separate 32-bit instance of Explorer on 64-bit Windows. This used to work in Windows Vista, but stopped working in Windows 7.
The ability to run a 32-bit instance of Explorer on 64-bit Windows was a feature in Windows Vista as a temporary solution in order to get Explorer to show both 64-bit and 32-bit Control Panel icons. In Windows Vista, there was a separate Control Panel inside Control Panel called "View 32-bit Control Panel Icons". This ran a separate copy of 32-bit Explorer so it could load the 32-bit Control Panel icons and let you use them.
However, this was only a temporary solution.
In Windows 7, the work was done to integrate the 32-bit Control Panel icons into the main Control Panel, so you didn't have the 32-bit Control Panel icons hanging out in some sort of 32-bit ghetto. In addition to making the Control Panel much prettier, it also made things much easier for users, since they didn't have to go digging into two Control Panels to find the icon they wanted.
Once that work was done, a standalone 32-bit copy of Explorer was no longer needed, and the code to support that configuration could be removed.