Upgraded, as in wiped the old OS completely clean and installed a fresh XP from scratch. I am
not a total idiot, after all.
Anyways, it seems to have been the native XP drivers that were the problem. Installing the new ones from Matrox fixed most of the offending issues. Scrolling is now almost smooth and almost as fast as under Win98, and the refresh problem has been halved, i.e. it only hurts the eyes half as much as before the new drivers, so it's tolerable.
Thanks, guys!
Edi