I just checked HP website to see if HP Solution Center was available for HP OfficeJet 6500 on Windows 7 and, unfortunately, just a laconic one megabyte USERHPNDU_2017.exe file is present.
Users on HP Website report that reinstalling the Vista software on Windows 7 running setup.exe in Vista compatibility mode should suffice. I'll report on it. Meanwhile I tried to run the already installed software setting the appropriate compatibility flags but it keeps on complaining about an incomplete configuration.
Luckily, that's just a testing Virtual Machine. I wouldn't like to pay-so-much for a Windows upgrade just to discover, once more, that some of my hardware is not compatible.