PC Desktops with Firewire
You are more likely to find PC desktops with built-in firewire that you are PC laptops. The most important consideration when using a firewire audio interface is the firewire chipset of your firewire connection. You'll find that this is generally a requirement of any manufacturer of any firewire audio interface. Different firewire chipsets handle data differently, and some are better suited to the requirements of streaming multi-channel real-time audio.
While Macs with built-in firewire ports do use a supported firewire chipset, finding a PC desktop with built-in firewire that uses a supported firewire chipset can be difficult. Firewire chipset is often not something that is listed in available tech specs for PC's and PC motherboards, so it's highly recommended that you do some research in various audio recording forums for suggestions on what PC's with built-in firewire people are having success with. In the event that you do not have a firewire connection, or you have a built-in firewire connection but it has an un-supported firewire chipset, you can in most cases easily add a firewire expansion card which uses a supported chipset.
NOTE: You may be able to find Firewire to USB adapters, and they may work for connecting external hard drives or cameras and other peripherals, but generally speaking, they will NOT work for audio interfaces.
To add a firewire expansion card, you'll need to have an available PCI Express or PCI slot. You will need to examine your computer's motherboard, or the documentation that came with your computer in order to determine what kind of slots you have available. Below is a picture detailing the different visual appearances of PCI Express and PCI slots:
A PCIe card can be inserted into a slot of its own size or larger. For example, a PCIe x1 card can fit into a PCIe x4 and x16 card; however, a PCIe x4 card cannot fit into a PCIe x1 card.
NOTE: If your computer has both PCIe and PCI cards, you would want to make use of the PCIe card, as the PCI Express architecture will offer much improved bandwidth over PCI. Since PCI is an older legacy standard that has been superseded by PCI Express, on a computer with both PCIe and PCI slots, the PCI slot must transmit data through a "bridge chip", decreasing bandwidth and resulting in problematic behavior and reduced performance. For this reason PreSonus recommends using PCIe FireWire solutions whenever possible. For more information on this, check out this article from Intel.
A complete list of FireWired Cards is available available here in this PDF.
Desktop Firewire Cards
For PC desktops, here are a few cards on our Approved Firewire Cards list from different retailers. You will either need a PCI (legacy) or PCIe (PCI express) card, depending on your computer:
Legacy PCI cards:
This Belkin F5u504 PCIe card may also work and you might find it locally at Best Buy:
Again, chipset is the important thing here, so always double check if possible.