FireWire
FireWire was tricky. The PowerBook 3400c officially has two 16-bit PCMCIA expansion card slots. However FireWire cards only come on 32-bit CardBus cards (which are shaped similar to PCMCIA but use a faster bus and are notched differently so they dont fit in old slots).
The PowerBook 3400c uses a Texas Instruments PC Card controller that is actually CardBus compliant. As Quoted from Apple Tech Article Below:
"The PowerBook 3400 computer utilizes an industry-standard Texas Instruments PCI1130 PCI to CardBus controller to act as the bridge between the system PCI bus and each of the PC Card Slots. Although the TI device is a cardbus-capable controller, the PowerBook 3400 does not support CardBus cards due to the requirement of a specialized PC Card socket, which is not part of the system."
Sounds promising.
I bought a VST FireWire CardBus card. Tried to stick it in. Sure enough, it didn't fit. How annoying. But I wasn't even about to pay $99 for MCE's CardBus Conversion (I still haven't).
The author of The 3400c is CardBus Compliant website had some limited success in getting his 3400c to recognize a USB CardBus card. However he had zero success with the very VST CardBus card that I had purchased. Even more challenge!
I decided to attack the most infuriating problem first. Why exactly didnt this card fit? It looked exactly the same as my other PCMCIA cards, namely my Diamond Supra PC Card 56k Faxmodem. The two cards were nearly identical, so I examined them closer for any minute differences.
And differences did I find. On the end of the card that is inserted into the comptuer, there are notches on both ends. One end is U shaped, the other is shaped like an L. On the end shaped like an L, the notch was slightly fatter, and not quite as long as the PCMCIA card on the CardBus card. Success! I shaved off all the plastic to make sure it would work.
Now the card fits almost perfectly into the bottom slot, and another ray of hope, an unrecognized card showed up on the desktop! Super! I then went to VST's website and downloaded the drivers for my Card. Installed them, and success the card was now recognized as a VST FireWire Card!
At this point I still had Mac OS 8.6 installed. I tried gettin the iPod to show up on the desktop. No such luck. I then tried FireWire Target Disk mode from my PowerBook G4 to show up on the 3400c desktop. Still no luck.
So thats when I upgraded to Mac OS 9.2.2. (See Mac OS 9.2.2 section).
After that things still didn't want to mount. I had the iPod install CD and ran it, which installed FireWire extensions and iTunes 2. I made sure Mac OS 9's FireWire extensiosn were enabled, because I discovered they werent by default (which makes sense since the 3400c isn't supposed to have FireWire ports).
Now the computer recognizes my iPod and works perfectly (See iPod Section), my DV Camera (See Final Cut Pro section), and when I connected it to my PowerBook G4 with FireWire Disk mode, it worked too (see pic below). As time goes on I will try more and more FireWire devices to ensure compatibility.

Some issues have made themselves apparent. If I try to boot or reboot the 3400c with the FireWire card inserted, the card won't be recognized. Not only that, the card won't eject eitehr, so I have to force it out, which isnt good, so I try not to do this too often. Also, the card still doesn't fit in the top slot.