You will need additional software form HP for the buttons on the scanner to work. Unfortunately that scanner is now 5+ years old, and has no drivers for anything beyond Vista from HP (an no server operating systems at all).
The driver you used from MS is actually dated 2006 as well, and you're technically using a Windows 7 driver (again, no server OS's are supported) that just adds enough capability to do the scan using Windows' built-in scanning sub-system, and doesn't have the driver required to recognize the buttons themselves.
You could try forcing in an application or alike extracted from the Vista 64-bit driver, but I wouldn't expect much luck.
Your better bet may be to use an XP VM like VirtualBox, VMWare, or use Hyper-V and install the XP drivers into that for use with the scanner. Note: Windows Server 2008 doesn't include the "XP Mode" licensing Windows 7 does, so you need an extra XP license to remain legit.