I think that BIOS can enable support for USB keyboards, but with USB mouses the situation is different... I know a couple of DOS drivers... not sure if they will work in Windows 3.x
yes, some can at least emulate a USB keyboard, but that is just for the part of boot time that the bios controlls, once it hands over control to an OS, that OS needs it's own drivers.
Comments
http://www.oldfiles.org.uk/powerload/
user: drivers
pass: all
Anyway, just get a PS2 converter, theres no reason that it needs to be USB.
Yeah... those things are cheap.
There ARE DOS drivers that can use USB mice, but none for Windows 3.1X AFAIK.