try 'lsmod' to see what driver is loaded. also, check if the usbdevfs is mounted by 'cat /proc/mounts'

The USB subsystem in linux works like this :

a set of core drivers needs to be loaded which handles the hardware detection stuff(plug/unplug). These information some how would be presented in the usbdevfs and there is a hotplug program/deamon that would handle the actual loading/unloading of the correct device drivers(and subsequent stuff). All three must be running properly for USB to work.