I was not aware the Vista was not still being supported in fact Apr 2017 is the official version of the deadline (providing SP1 has been installed - though as I understand it, SP2 encompasses all previous updates). see here
However I suspect the the HP incarnation has added another layer of complexity.
Unless the user is adept at searching the registry I doubt there is much else that can be done. Setting the second user to Administrator should be within most peoples' capability. It will be in the the Control Panel.
Control Panel > User Acounts and Family Safety > Double Click the User account > Change Account type > check Administrator. See how that performs.

Linux looks to me to be a huge learning curve for a user that just wants the beast to work.

And just to show how easy it is to be fooled: I keep the Vista machine plugged into a second screen and if that screen is not switched on and the Control Panel is not showing - panic! Until the second screen is switched on. Doh!