From the way your question is asked, I think you may be
talking about Boot Camp. I haven't done it because Apple
don't support 64-bit Vista (or XP) in Boot Camp yet. I
was actually somewhat disappointed when Apple didn't
include 64-bit Boot Camp with Leopard.
As you suspect, others have done so, with what I understand
is limited success. If you get no direct response, a forum
search will likely turn up a few instructions.
What I _have_ done is install Vista-64 as a VMware VM.
That works well enough for me, at least as well as Vista
_can_ work. I do most of my real Windows work in an
XP-64 VM, which is pretty solid.