http://www.microsoft.com/windowsvista/1033/ordermedia
That's the link where you can order a x64 disc.
(when I did it it cost about $10-$15, I forget,
shipped to anywhere in the USA via snail-mail).
You have to give it your existing Vista Key and
edition information as a prerequisite. I don't
know if there'd be any restriction about using
an academic or OEM or other class of original
key to obtain and be able to activate the
x64 edition. The disc they send you
is probably generic in that it'll contain
virtually all the VISTA install editions --
Home premium, Business, Ultimate, etc, and
you can install any of them as a trial, though
you can only activate the version that your
preexisting key authorizes.
That is the most common way for a 'cheap'
x64 upgrade if you already have some
x32 license/disc but were unable to get x64
media from your vendor. Most license keys
are usable with EITHER x32 or x64, your
choice.
Yes check your university software / book store
prices, a lot of time it's cheap or free for
academic prices, and there is no single
"academic price" it varies from institution to
institution, some are even free or like $15.
Of course being a student you do qualify
for the generic academic license so if you
do find a better deal online or from some
other university store or whatever you should
be able to get it from there instead given
your student credentials.
Also if you know someone already with the
x64 install disc for any retail or academic
version of vista you might just borrow / copy
it for your test / install; once you own a
x32 key you're typically fully licensed to
own and operate x64, it's just that they
don't by default give you the media, so
wherever / however you do get it is just
fine since you're already licensed to have it.
You might also check out certain CS classes
that have vista as a prerequisite, maybe you
can get it cheaper / free if you enroll in one
of those or at least you can get info from
the lab if they've had any known problems
with x64 activation / use on the academic
licenses etc.