Buy a serial DB-9 to USB connector from USB GEAR and get their software XP.zip from their site (less than $20).
Install XP.exe (works with Windows 98 & XP, Vista & Mac also available). Plug DB-9 to cable, and cable to computer. In ExpressScribe, go to settings/control, XP creates a new COM port. Pick the last one, run the setup wizard. That's it.
If it seems that there's only 2 functions available on yr pedal, that's because the wire on pin #9 has to be moved to pin #8 (pins are numbered but it's minuscule). Rerun the setup wizard.