Useful links

Software Mechanics
They have a plotter driver named WinLINE which supports wide range of the HPGL and HPGL/2 plotters and works under all kinds of Windows.

HP Computer Museum
A collection of old Hewlett-Packard computer hardware, software, documentation and other marketing materials from HP's early years in the computer industry.

Translates X-Y analog plotter output into a stream of HP-GL commands.

The great software download site.