2.19 How do I go about setting my path to hpbin.sys?

You can add HPBIN.SYS to your HPPATH at the end with the command:

SETVAR HPPATH HPPATH+",HPBIN.SYS"

or at the front with the command:

SETVAR HPPATH "HPBIN.SYS,"+HPPATH

The above is more readable, but you can also do:

setvar hppath "!hppath,HPBIN.SYS" /* appended */
setvar hppath "HPBIN.SYS,!hppath" /* prepended */

You can also use POSIX HFS syntax in HPPATH:

setvar HPPATH HPPATH+"/SYS/HPBIN"

Using POSIX HFS syntax in HPPATH causes POSIX name rules to apply to the name of the file you are trying to execute.