Update on my lockdown diversion: this morning it would not boot, freezing mid-post, unresponsive to 3-finger salute. Thought I might have done something terrible by impatiently hot-plugging a ps/2 mouse yesterday. (the k9mm-v is usb-finicky).
I decided to try clearing the cmos. Shifting the sound card and some sata cables out of the way, I had just enough room to grasp the jumper (MrsD.'s cosmetic tweezers not up to the job). After it came back to life, I ran updates on Fedora 31, installed xfce desktop to it and turned my ministrations to xp, which was mysteriously ignored by the FC31 grub two -- it's now a subitem in the Windows 7 boot menu, listed as "fucking old windows" or words to that effect. The OS that dares not speak its name.
Where Win7 was running quite snappily yesterday immediately after the install, I found it sluggish, and messed around with the memory cache settings, which seems to have helped. No doubt Win7 wants a lot more ram than xp, but the mb is maxed out at 2G :-( .
I did a brief trial run of Dead Island Riptide on it. It ran about as well as under xp on this old rig, which is to say not great, but playable. I need better headphones though.