I am pretty much in the same boat as you are scott, in that I'm not much of an expert on either one either.
In my research, however, it seems that the advantage to the firewire is an out-of-the-box recording set-up. They usually come with built in mic pres and most even come with some kind of software, so for the price it is the quickest way to start recording.
The disadvantage of the firewire box is the other side of the coin of the advantage - that you are pretty much stuck with the built in mic pres, so if you eventually want to get more serious about recording, then you might as well buy a new interface in addition to new mic pres. Also, most firewire interfaces only work with XP, which is a disadvantage to people with older comps like me who still use Win2K.
The advantage of the PCI interface is that it really gives you a more professional interface. The Delta44 for example (my personal choice) is simply a straightforward audio interface, with decent A to D converters and balanced inputs/outputs.
The big disadvantage here is price, because in addition to the interface you still have to buy mic pres, mixer board, etc., that you are going to use to record. So, cost wise, if you buy the PCI interface in general you still have a long way to go to record - though in the long run it may very well see more use than a firewire box, IMO.
For portable use, firewire is hard to beat because everything tends to be more integrated.