Firewire (IEEE 1394) and USB (Universal Serial Bus) are two separate high-speed bus technologies that allow multiple devices to be connected to a computer. The two technologies are not integrated, and it is not possible to connect a USB device to a Firewire port either directly or through the use of a Firewire to USB adapter.

However, that doesn't mean that your Firewire devices are useless if you have a USB port, or vice versa. Although a Firewire to USB adapter does not exist, and cannot exist because of differences in the two technologies, several companies do provide dual Firewire/USB hubs. This type of device has two ports in a single hub, which may be either external or internal; one for Firewire and one for USB - allowing either type of device to function. The combination hub is actually two separate ports combined into a single form factor for convenience; there is no conversion between Firewire and USB taking place when you use one of these hubs.

Another alternative is simply to add two separate cards, assuming your computer has enough available slots. Firewire and USB cards are both coming down in price, and adding whichever one is missing should not represent a major expense.