Damage using a serial cable to connect 2 PC's?

Hello again,

I have a basic question: is there any way I can damage either
the serial port circuitry OR the MB itself by incorrectly (wrong
pinouts, bad cable, link program doing something to the machine,
etc.) when trying if a DB-9 serial cable with a null modem
adapter will work?

I am asking because my "USB on a 166MHz PI from 1997" experiment
failed - there is no power going to the MB USB port connector
pins - so I have given up. I am interested in trying a serial
cable connection - Total Commander has it built in, and I also
have several other DOS and Win programs for it. But I don't want
to blow up either of the two computers.

Is there any danger?

Thanks.