I've thankfully solved this myself- with Google's help.(Has this forum "gone downhill" recently ? I used to have immediate replies to posts, but recently, I've had none or few, even at weekends.)I discovered that by following Tweakhound's advice on Vista services,link textI'd disabled SSDP Discovery, and IPsec Policy Agent services, and as soon as I re-enabled them,I could see my Xp machine on the Vista one,and share its folders.As before, though, I've been unable to see the Vista on the XP one. But that's less important.
Surface Pro (2017) vs Surface Pro 4