From the notes on the site, it looks like it should work ... the Organizer link cable is essential, as it's an "active" part.
For any modern XP PC, I'd be expecting it to have a 9 pin serial, if it has one at all, and most USB-Serial adapters are 9 pin, so you'd need a 9-25 pin AT adapter if that's the case.
Since the Psion presents as a DCE, and the PC is a DTE, a "null modem" cable is not required.