Firewure is a connection that tranfers at upto 400Mbps.
This compares to 480Mbps for USB2 and 12Mbps for USB1
For Digital Cameras you want either Firewire or USB2 and if your machine hasn't got one of these you will ned to buy a card that fits into a PCI slot. They are not all that expensive.
I would wait until you are sure what camera you are getting as they vary from both to one or the other of Firewire and USB2.