My 64bit Ubuntu shows in grub as I have both installed with something like
Ubuntu 8.10 kernel 2.6.27x on sda10 and Ubuntu 64 8.10 kernel 2.6.27x on sda 11.
I know both from the partition as I always keep a list of installed distros (I
have 11 or 12) or 64 is explicitly mentioned in grub whereas 32-bit does not
mention this. The same can be said for MEPIS 64 or Fedora 64. MEPIS says 64
right after the kernel (2.6.27-smp 64-bit) and Fedora says Fedora 64 before the
kernel and location. This is from grub as written by Ubuntu 8.10 but I get
similar results when grub is from MEPIS or similar. Fedora seems to ignore most
installed distros so I don't like their implementation much. I am doing this
from memory because I don't want to reboot, but it is generally correct.