I'm also having trouble with firewire... similar but not quite the same.

Asus P6T Deluxe V2 - i7 @ 920 (X58, ICH10R)

I just got my first firewire device- a G-Drive mini 500Gb HD from the Apple store. It works fine in Windows 7 & Vista (and XP on my old laptop).
but it won't work in leopard or snow leopard. in fact, when it's plugged in and turned on my boot gets stuck at the point where I enter the GUI (i always boot verbose) with the light blue screen. but as soon as I turn it off my logon window pops up. and if i plug it in after that, it just totally ignores it.
up till this point I had firewire disabled in my BIOS, but since I enabled it I see lines showing up in my boot text.
most of them are fine, but I was getting an error (no longer in my log file) which has corrected itself somehow but not affected my problem. I am getting a line with the vendor & product IDs as well as the GUID and its max speed telling me the device (on-board built-in port) is active.

My problem seems to be different since I am getting a valid GUID, but this thread seemed to be the most appropriate place to document my issue (and hopefully its resolution).

I've had trouble finding kexts for firewire other than the stock kexts with the retail disk.

Where did you find yours? And which guides have you followed? (my searches have not led to much beyond this post which is at all relevent to me)
my drive is claimed to be plug and play straight out of the box without any intallation of anythihng for max os X. it was true for windows...