Hello there, I've found this guide very useful for installations on windows server 2008. In terms of installation it really does not matter the installer architecture you are using, how ever if you have a windows x64 make sure you install qvs x64 to take full advantage of memory addressing.
I don't believe there are any special considerations for installing on Windows x64. Just download the x64 QVS and install. The only limitation has to do with reloads using ODBC. You must use 64bit ODBC drivers Not all datasources (MS Access, Lotus Domino, for example) provide 64bit ODBC drivers.