The only thing I've seen 66Mhz is Raid, Fibre Channel controllers, Gigabit Ethernet cards and a few SCSI adapters from LSI.
It wouldn't make much sense for them to make a 66Mhz firewire card as firewire doesn't even come close to approaching 33Mhz speed.
As far as a regular firewire card working in a 66Mhz slot, that depends on the system. If you are talking about the new dual AMD boards based on the MPx chipset, then no, there are no regular PCI cards that will work in those slots. There are some servers that have 64-bit, 66MHz slots on them that are backwards compatable with standard PCI cards, some models of Compaq Proliants to name a few.