You need Firewire (IEEE 1394) card. There is absoultely no other way. Here is one for you Ebuyer PCI Firewire 1394A Card with 3 External and 1 Internal Port £11.74 click here. You need to open up PC to fit the card, but fitting a PCI card is the easiest PC upgrade.
By the way, there is only a few D#digital video camrea models in the whole world use usb2 to transfer the video. panasonic nvgs50 (I also have one) is not one of them.