Wow, I thought firewire was pretty much standard on every computer for like the past 5-6 years. Yea, buy a firewire card, they are dirt cheap. It'll either slip into one of the PCI slots, or some pin on the motherboard (most likely if you get the card from the same manufacturer as the mobo). Good luck!
most of the firewire ports that come stock on mobo's suck anyway. Make sure you get a card with a Texas Instruments chipset. Some others will work sometimes, but if you want to be safe, just get the TI
ADS, Belkin and SIIG make super high quality ones, but I see a lot of people doing just fine on the 20 dollar ones from the regular computer megastores
Don't get a combo usb/fw, just get fw400 or fw800 depending on what your soundcard wants...I have heard but cannot confirm that combo fw400/fw800 cards are ok