Firewire is an external hardware serial bus protocol originally developed by Apple and has since been adopted as a hardware standard called IEEE 1394. Since it is now a standard, a lot of pc's as well as macs have integrated the protocol into their motherboards, as well as peripheral cards and devices. Firewire is merely the name trademarked by Apple for the technology.
Most motherboards now being released for the pc now have onboard firewire ports capable of 400 Mbs, the newer IEEE 1394b (called Firewire 800 by Apple) standard ups the data rate
to 800 Mbs - Gigabyte mobos seem to be the only pc mobos with 1394b while
Power Mac G5's have 1 Firewire 800 port and 2 Firewire 400. USB is another serial protocol also originally adopted by Apple in their early IMacs; both Firewire and USB were developed for Plug-and-play functionality.