Ivan,
Being a sensitive soul, I always look for areas of convergence and agreement and ours is "yes, it's broke".
I did delete/rename all those files, moved the NIC to another slot, and eventually the P&P reported "found new hardware" on restart #3,629 or so. It correctly identified the hardware, narrowed its eyes at the driver folder I whispered to it, and then said, "OK, I'll install those". The install proceeded routinely, until I was assured that my hardware was installed correctly and ready to use. XP then climbed back into its battered white van, sparked up a Marlboro and disappeared down the road in a cloud of diesel smoke.
Still no sign of the NIC in Device Manager though. At around the same time, though not necesarily associated with this process (I ran the Network Wizard thing a number of times as well), it started to 'see' the other PCs on the network. Also, internet access is OK and my router has picked up the PC's name in its device list. Only odd thing is that Zone Alarm reports the network adapter as in the "internet zone", and the network wizard warns me about being connected directly to the internet when it patently isn't. So, it has not quite installed the hardware, but it seems to function OK for my purposes for now so and everything is nicely stealthed on the Symantec security scan, so I'll leave it be. I'll have to get the road drill out when I need to set static IPs or something else I need a network connection icon for.
On the other hand, it's an excuse to take it to bits and rebuild it...