On Windows, go to Control Panel → Programs and Features → Uninstall “Bootcamp”. Then restart. Note: Your keyboard and touchpad will revert to basic Windows drivers.
Either copy the file from a USB drive, DVD, or downloaded folder. Put it on your Windows desktop for easy access. Bootcamp 3.0 64-bit.exe Download
Even if you don’t have the DVD, Bootcamp Assistant on macOS Snow Leopard or Lion can download the driver package automatically: On Windows, go to Control Panel → Programs
Technically no, but some users report success using the 64-bit installer in compatibility mode. However, many core drivers will fail. Use at your own risk. Bootcamp 3.0 64-bit.exe Download