a) you can run a 32bit distro w/ a 32bit kernel just fine.
but afaik, nvidias 32bit xorg-driver can't talk to nvidias 64bit kernel
this means you need at least a 64bit xorg, and everything that's
required for a 64bit xorg.
32bit apps can connect to the 64bit xorg.
of course you can use an open-source driver, which does not rely kernel
but i don't see any advantage in having a 32bit distro, and an 64bit kernel.