You must not try to put the firewire ( 1394 ) cable to any usb connection.
If you want to use the internal connection for firewire, you will need to buy an internal pci firewire card, like click here. This will fit into one of your 3 large PCI slots and you connect the header cable to the internal connection on the card.
Make sure the internal connection ( end of wire ) and the connection on the card match. Some take the 6 pin lead straight to a camera, some are like the header pins on a motherboard. e.g. pins sticking up.