After adding usb device,when I use lsusb, I can see my webcam listed but nothing under /proc/bus/usb/ there is nothing?
mount usbfs, mount -t usbfs none /proc/bus/usb. You can chown them to your user if you're not running as root.
can one connect/disconnect usb devices, and XP manages this without manual "mount" intervention from host os?
usb is possible. for pci, it needs extra work (Januar 2008), check qemu's usage documentation on usb.