1) You can read 9121 diskettes on a MS-DOS or Windows machine using the LIFUTILS software. This software was made by HP and then released as freeware to help users migrating from obsolete platforms.
2) Using the LIFUTILS you can read data files from the floppies and then extract the data using some conversion utility that you can write. The difficulty of the task depends on how the data files are constructed.
3) Reading program files is more tricky as they are stored using some binary encoding scheme. In fact moving files between HP-85 and the HP-86 requires some kind of conversion which occurs automatically. Other computers (e.g. HP-75) have a command to convert between binary BASIC programs and ASCII files, but I am not aware of such a program for the HP-86.
If you have a serial interface on your HP-86 you try connecting a PC to the other end and run a terminal emulator program like kermit or HyperTerm. Then you PLIST
the program on the serial "printer".
This is a one-way operation though, I do not know how you can get an ASCII BASIC program down to the HP-86.
4) Program rewriting. To run the software on new machines you will have to convert them. The effort involved depends on how bad the programing style of the original programmer was and the length of the program. Unfortunately the HP-86 BASIC encouraged writing attrocious programs (e.g. the various programs released by HP).
Send me email if you need additional information or assistance.
**vp