IEEE1394 is the proper name for Firewire before apple 'branded' it
You either have an onboard 1394 controller or a Soundblaster Audigy soundcard, hence it shows here.
Firewire is a theoretical 400Mb/s, Firewire-800 is (you guessed it) 800Mb/s.
USB is 12Mb/s, USB2 is 480Mb/s.
Firewire is mostly used as an alternative to USB2 for external HDDs (in most cases it performs better than USB2 despite the theoretical 80Mb/s less bandwidth. It is also used extensively in the A/V world for digital camcorders etc, and is much more widespread than USB here.
As Choknuti says, you can use Firewire to network PCs under WinXP. Its very fast, (I have used it myself) but of course the max cable run is around 10m and its only point to point, Firewire Hubs (similar to USB hubs in design) dont allow you to network more than 1 PC by it.
You can Daisy chain one computer to the next if they all have 2 or more ports, and you bridge the connections with windows tho
Basically Firewire is Apples alternative to USB, and is imho superior, though it pains me to support apple...