Here you can download the original PCMIDI utilities and manual as well as the newer version quick setup guide.
Keep in mind no drivers are needed for DOS.
Windows 3.x , 9x and ME include the "Roland MPU-401" driver which works perfectly with PCMIDI.

 Original PCMIDI manual    
 Original PCMIDI utilities disk image and files (for historical reasons)    
 New PCMIDI Quick Setup Guide (all you really need!)    
 Windows 9x/ME MPU-401 MultiPort drivers
(gets rid of annoying "this device is used by another application" message)

 All of the above files in a single package