lets setup a scenario so that you would understand it a little better...

i have a system with usb2 compatible ports... now i have 2 devices .. a backup harddrive, and a camera
Backup harddrive USB2
Camera USB1.1

now i use the backup hardrive to backup some data.. backing up complete... now i need some conferencing on the internet.... i plug out the USB2 hdd and then plugin the USB1.1 camera... and WOUALA!!! it works just fine..