Onboard NIC's can be a barsteward, i once an issue when playing games online the sound would bomb out with squeaks and garbles then the pc would lock up solid.... spent literally months trying to figure it out and it was down to the onboard NIC was bad in some way..
u could try turning off the nic in the bios and see if that sorts out the mouse problem, if it does try and get your hands on a pci based NIC they can be picked up pretty cheap from ebay
