In case it helps anyone to get the hboot driver installed under x64 this is what I had to do (copied from Modaco forum):
Open Device Manager, right click the ADB device and click Uninstall
Tick Delete the driver software for this device. and click OK.
Download
USB Deview and open it.
Sort the list by Serial Number and look for anything with HT at the start (e.g. HT00GPL00000).
Highlight them and click Uninstall Selected Devices in the top left (looks like a recycle bin).
Unplug the phone and then plug it back in.
Open Device Manager, right click the ADB device and click Update Driver Software...
Click Browse my computer for driver software.
Click Let me pick from a list of device drivers on my computer.
Select Show All Devices and click Next.
Click Have Disk...
Click Browse...
Browse to your desktop and go into the usb_driver folder.
Select android_winusb.inf, click OK and then select Android Composite ADB Interface.
Click Next, when the Update Driver Warning appears click Yes.
If all is done correctly, it should say Windows has successfully updated your driver software. Click Close to finish.
This worked although I obviously used the modified driver instead