I was actually wrong in my first post, about the name. i.LINK is Sony's name, Firewire is the Apple name, and IEEE-1394 is how it is known generically. But the important thing is, it's just different names for the same interface.
Sorry, maybe I wasn't clear enough about my advice the first time. What I meant is this:
It sounds like on your computer, you don't have a port to accept the i.LINK/FireWire cable. Right? So, the way to get an i.LINK/FireWire port on your computer is to get a card. This will not replace your i.LINK cable; rather, it is a device to add a port which will accept your cable.
Yes, you were quite correct: to insert this card, you will need to remove a side panel of the case. (I think so, because an advertisement for this machine talked about an internally lit side panel. But I could be wrong.) At any rate, at the back of the case there should be some small screws (and possibly some slide latches) holding this side panel (or the whole case, it may be) together. I'm not quite sure, but since you were able to add memory to your Sony, I'm confident in your ability to figure this out.
When you have this off, you will be looking at the motherboard of the computer, with all its components attached to it. You should see a row of slots all together, some shorter, some longer. Which FireWire card you get, will determine which slot you put it in. There are people on this forum who can explain that to you better than I can. Anyway, above each slot, you'll notice an L-shaped metal (sometimes plastic) strip covering a slot; these little covers are often held in place by a screw. When you remove the cover, the face of your card will take its place. So, from the outside, you'll just see the face of the card, and the ports it has.
I hope I may have clarified a few things for you. If not, feel free to fire away with more questions.