I have been using the Windows Vista 64 bit driver on Windows 7 64 Ultimate for a couple of years now. It works flawlessly!
This driver is available from the HP support site. I don't recall needing to pull any tricks to get this driver on Windows 7, but there is something at the back of my mind saying I needed to rename something - except everything looks as though it's native HP.
Enjoy it's a great A3 printer that can be picked up secondhand as people discover their printer isn't supported within Windows 7 (and maybe W8?)