I believe there are PCI cards you can buy for most PCs. Something like this I think:

http://www.amazon.com/dp/B000AW1G4M/?tag=r06fa-20

I'm sure someone else here can fill you in better.

Check into Siig cards. They use an Audio-Friendly TI Firewire chipset and are darn cheap for what you get.

look at http://www.newegg.com

Cheers-
Jeremy

i believe i have a PCI-express slot in my computer, does that change anything?

i was looking for something that is compatible with any of the presonus firestudio line... does that change anything like would I need an additional soundcard as well?

Siig makes PCIe 1394 adapters. Check with the Presonus website for compatibility issues but I doubt it.

would i want a 400 or 800 firewire card?

I use combo 400/800 cards. Most manufacturers want you to have one or the other but I've never had any issues.

Do NOT use combo cards with USB on them. Ever. Really.