Success, of sorts. I twigged that my internal modem may have been hogging the COM ports and sure enough, yanking it out prompted Win 95 to detect my Psion. Hmm, hardly an ideal situation, though - I tend to use my modem quite regularly! Fortunately I have two separate OS partitions, a Win 95 for games and an NT4 or serious stuff. So if I can't solve these hardware conflicts, I'll install the Psion onto Win 95 only and uninstall the modem. It's not an ideal situation, but it'll have to do for now.
In a perverse way, I actually enjoy grappling with this sort of problem. My room looks like the aftermath of a bomb in a branch of Dixons - bit of PC everywhere, wires strewn precariously across the floor. Now all I have to do is get my NT workstation partition up again so that I can salvage my email folders before I wipe and reinstall yet again (it's the only humane option). Shame I don't have time to do it today; I'm off to a house-warming party in Birmingham. It seem to be the season for it - I guess people move house in summer/autumn, and delay the party until after Christmas. Should be fun, anyway.