Don't know how well/stable Bioshock will run on a 64 bit OS, sorry. Recommend checking some bioshock forums.
But I'm sure it won't have any impact on how it looks (your system looks strong enough to run with settings on high anyway... I doubt you're cutting things so fine that using your full 4gb under 64bit vs the ~3.3Gb under 32bit will make any difference).
I completed Bioshock on Vista 64bit under full settings and it worked fine for me. It crashed once but that was due to a programming error on Bioshock not Vista.
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