usually it is a PCI slot - expansion card which you mount on the motherboard so that you can connect to other firewire devices like sound cards, videco cams at speeds similar to a usb 2 connection (debatable of course)
firewire cards come with Texas Instruments or Via chipsets or even creative chipsets also. it usually will depend on what is your purpose. for audio recording it is a safe bet to use a T.I. chipset. although it is best to check with the peripherals you plan to use. meron din el cheapo firewire sa cdr king less than 500 pesos. but no guarantee if it will work with the device you plan to use.
you can try the audio/pc classifieds here at this forum or you may try tipidpc.com. but be sure of the specification you need and be aware of what you are getting into.