Amd64 + proprietary driver

[Levi Bard <levi@bard.sytes.net>]

Question: If I run a 64 bit kernel with a 32-bit userspace, how does 
that work with something like nvidia's graphics drivers, which have a 
(source-based) kernel module component and (binary) userland libraries?  
Can I use the 32-bit kernel module with the 64-bit kernel?  Or do I have 
to build the kernel module as 64-bit, then install the 32-bit libraries?