Hi
Most Motherboards have an Internal USB header on the motherboard to connect another usb socket (ie some cases have USB connectors in the front) so that will be why you see 2 instances of the usb controller
You can disable/enable then in the bios
Some motherboards have a riser slot (normaly a small dark brown slot next to the agp slot) this is for things like modems/network cards ect didnt catch on as it used CPU cycles and used software rather than hardware control (I think)
Hope this helps
MaV