This is from the Precision Pro 2 CD - works fine with my 6520c -
I don't know which of the files is considered the driver so I've zipped the entire directory including the help file - good luck.
The following files are found inside the driver download file.
|HPSJUSB.SYS||20.4 KB||7 May 1998|
|HPSCNMGR.HLP||35.6 KB||11 Feb 1999|
|Hpscnmgr.dll||262.1 KB||25 Jun 1999|
|HPSJCLAS.DLL||20.6 KB||15 Apr 1996|
|reg32.dll||32.8 KB||25 Jun 1999|
|vhpscand.vxd||11.9 KB||21 Aug 1998|
|scanjet.in||4.6 KB||25 Jun 1999|
|hpscntst.dll||389.1 KB||25 Jun 1999|
|hpsj32.dll||32.8 KB||25 Jun 1999|
|hpsj1695.dll||928 bytes||19 Feb 1999|
|HPSJRFSH.VXD||8.4 KB||29 Oct 1997|