If you are going from 32 bit to 64 bit, you have to do a Custom (clean) install. The reason is, you cannot run the x64 setup routine from within a 32 bit version. You can not do an in-place Upgrade unless you run the setup from within the previous OS.
Therefore, you will have to reinstall all you programs and backup you files.
Also you cannot do an in-place upgrade from Vista Home Premium to Win 7 Pro. So the process will basically be the same whether you go with 32 or 64 bit.