I have to agree with pretty much everything said so far. I do prefer the mid-ATX cases over the smaller ones, simply for upgradeability.
The only thing I would comment on is to perhaps go for an expansion card (1394) manufactured by a reputable company. You do get what you pay for... And if you're transferring important data, I wouldn't want to go risking it! Make sure it's Vista-compatible, also, otherwise you may very well end up hitting a brick wall with driver issues.