I also have a MR-8100 from an original owner with all the original docs and the original 5.25" Floppy disk!
However its easier to use a 3rd part programming software from GFC Software. See all the links below to get you started.
Carefully and thoroughly read the instructions on Repeater Builder website for the MR8100. This is the most details site found.
comprehensive MR-8100 downloads -->
Technical Information on the UNIDEN Scanning Mobile Receiver model MR8100
DOSBox (x86 emulator) -->
DOSBox, an x86 emulator with DOS
PSCAN software -->
GFC Software Product List
As 'NoSoup4U' stated, You first download DOSBox software to you newer Windows Computer. DOSBox is a (x86 emulator) so it allows older software to run in a virtual memory space essential tricking it in to think your running on an old x8C Intel based computer (1990's era).
I run DOSBox on Windows10. You start up DOSBox, execute the commands to start up the PSCAN software.
One item which you will require is the either just a
[DB9 Female to Female Serial cable]
www.yourcablestore.com
or
a DB9 Mal to Female cable PLUS a [DB9 Female to Female adapter] also called a "gender bender"
DB9 F/F, Mini Gender ChangerSupport Files: Dimensions Diagram (Oct 15, 2012)
www.monoprice.com
One end of this DB9 mates with the MR8100's male serial port. The other end of the DB9 can be connected with a DB9 to USB serial connector. The USB to DB9 serial cable that I use is Model XS8801 from USConverters.com.
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USB Serial Adapter – Windows 10 Compatible High-Speed RS232 adapter
*This RS232 serial cable can also work with any Uniden scanner that has a DB9 Female connection on the back of the unit. BC898T, BC796D etc.