PCI-E x1 Firewire cards are rare and tend to be expensive. Nevertheless, almost all regular PCI Firewire cards work on hackintoshes much more often than not. It's easier to replace your PCI NIC with a PCI-E x1 NIC and then buy a regular PCI Firewire card for $10 (delivery included) on eBay. The following PCI-E x1 NIC works like a charm on 10.5.8: TP-Link TG-3468. I'm sure it works on 10.6.4 as well, but you may need to check it. It's a very inexpensive NIC.