It appears that my Vivanco Mobile Optical Mouse is incompatible on some deep harware level with this crappy old PPro/Intel mobo, as it makes the pointer jumpy so that it's virtually unusable in precision-taking jobs (such as ones done in The GIMP). Even my trusty old middle button patch refused to work with this setup.

Then there's the Mitsumi Sony Quick Scroll Mouse/MemoryStick reader combo, whose MemoryStick reader won't work; it's just as one dead with the MS inserted.

However, this time I'm extremely lucky with my hardware problems, in that the mouse side of the Sony combo does work, and even the middle button functions as expected! So I'm using this old rat as my pointing device for the time being. It's quite big and clumsy in hand, but at least it works!

And no, I don't have any knowledge of whether or not this is Linux-specific, so sorry for the somewhat misleading title, but I figured that maybe someone who suspects it is comes googlin' in here and finds this data useful.