You may not do what Microsoft call an "In Place Upgrade" (which preserves apps and settings) from 32 bit to 64 bit. You may, however, do a "Custom Install" - this puts your existing 32 bit installation/data into a folder called "WINDOWS_OLD". The 64 bit install will be clean, you will (with a few exceptions) not be able to run apps from the Windows_Old folder, so you'll have to do the reinstall routine. But your Data will be preserved - retrievable from the Windows_Old folder.
If you want to set up a Dual Boot - You'll need to set up a separate drove or partition. Then install 64 bit to that. Once W7 64 is all finished, you may then change the config to dual boot with the other W7 install.