I've got MVP3 and KT100 motherboards in my house. USB works
absolutely fine on them.

Did you try the VIA VT6202 USB 2.0 chip with the VIA VA-503+ mobo,
based on the MVP3? I got a blank screen and no disk activity when I
did, and the particular USB card was from a Soyo BayOne Professional
front panel USB kit, which worked with every other mobo I tried,
except for an old 486 one. It even worked in a VIA PA-2007, whose
chipset is the predecessor to the MVP3, the VP2.

No, just plain ol' 1.1 for the time being.