So, with the data sent through 2 networkcards, and the laptop's usb port, everything is o.k.
That excludes the harddisk-mainboard-memory-mp3 player of being the problem.
Are you using other devices (mouse-keyboard-memory reader etc.) on other usb ports, remove 'm, try a ps2 mouse
You even could remove the avermediacard, to see if that helps. If it does, replacing it in another slot may help staying rid of the problem.
There's something wrong with that usb hub, at least the way windows implements it.
Maybe this will help,
http://support.microsoft.com/?kbid=908673