I came across this forum in search for answers as to why my hp scanjet G3010 was having issues installing in windows vista x64.
The problem for me was that after installing the x64 dvdrom, unsinstalling it, downloading the latest version from the HP site, I would come up with the same problem. Formatting and re-installing windows x64 did not fix the issue (Which I never had with the 32bit version of vista ultimate). The problem was that when I plugged in the USB cable at the designated time, windows would come up with an error stating that the device was undefined. It would not load a driver for that device.
I read several threads here from people who were having the same issue, but no one had an answer. So I went to the HP site and began the process of speaking with a an HP rep online. When it asked for my serial number for the scanner I pulled it out from its slot and, for whatever reason, decided to turn the power switch off and on again. The scanner powered up. I had unplugged the USB cable and uninstalled the software previouse to this. When I re-installed and plugged in the USB when the instalwiz asked me to, it worked. Problem solved.
If anyone is still having this issue, they may try these steps:
Do an uninstall for HP photojet
Unplug the USB cable
Turn the scanner's power off and on again (At this point the scanner remained powered on).
Re-install with the vista x64 dvd.
plug in the USB cable when it instructs you to.
It worked for me. I just thought I'd make an account and share this info with anyone who might still be having a problem.