It would be nice if the script would work for tinycore64 as well. I tried but linux-headers-3.0.21-tinycore64.tcz was missing in the repo. Tried with linux-headers-3.0.21-tinycore.tcz but got a lot of errors. The virtualbox-source should perhaps be a different one for 64 bit as well?
I have modified the script somewhat so it should work on 64bit as well, but am running into compilation issues running it within a 64 bit install. On previous versions 3.x I was able to cross-compile while running from a 32-bit kernel. I'll post my results when I get a chance. Also, last I remember, on 3.x I couldn't actually get the 64 bit modules to run with the virtualbox-ose provided from the repo, as it was compiled in a 32-bit environment with the 32-bit libs. It's been a while though and I unfortunately lost my previous installation of TC when a thumb drive went belly up.
Right now I'm running 32-bit with PAE on the Host (with 16GB of RAM) and 64-bit Guests underneath. Performance is equivilent to VMWare Workstation 64 bit on Ubuntu, so I don't think 64-bit is necissary unless you start getting into really large memory situations for your guests. (Right now all my guests run 4GB and under. I'm not sure what the limitations of PAE are as well.
Also, there are lots of modules that aren't compiled for 64-bit yet. I heard rumor there was going to be a 64-bit repo at some point, in the forums somewhere. I would be willing to contribute significant time to getting everything compiled if this ever happens. With everything mixed its just hard to disseminate which installs are x86_x64 cross compiled or native or 64-bit only.