Thinkpad W500 two-finger-scrollable touchpad

So this beautiful 1900x1200-resolution machine, the last of it's kind I believe, can get pretty stubborn with its touchpad.  The official Synaptics ultraNAV driver from Lenovo doesn't offer this highly-productive feature for this model (maybe too old/discontinued).  Slapping on a Linux distribution doesn't help either (Ubuntu's 12.04 and 16.04 attempts only).

Also the last of it's kind.  The knob-textured upgrade of the W510+ would wear away; throwing the touchpad sensitivity out of whack. This baby, by contrast, lives forever.

The solution I found that did work, was a bit of a hack found at the thinkpads.com forum.  Too old of a thread (and too lazy to create an account) to contribute over there; thus this post.  Particularly, since it's Win7 x64 I'm running, the version 15.0.9 driver from the sp47815.exe package at hp.com was the winning ticket.  I don't know about the Windows XP version.