Firewire networking is limited to 15ft. Anything more than that & you should expect to see some serious drops in transfer rate (due to noise) unless you use a repeater. With a decent repeater, you're looking at a max of around 240ft.
Also, firewire is only for IP, so you can forget expanding to NetBEUI IPX etc should that be needed at any stage.
Firewire networking is also limited to the latest versions of windows, unless you use
UniBrain.
I've never seen more than two machines connected in a firewire network, but in theory, it's all good. Each machine would have a static IP, and the internet connection could even be shared by ICS.
If speed is more of an issue than cost is, it's possible to get a firewire-fiber-convertor, so the only part about firewire LAN I'm not sure about, is the hub. A fiber hub works the same way an RJ45 does. I think a firewire should do the same, but you'd need to be careful, as a USB hub doesn't (USB hubs have their own ID etc). However, USB networking still isn't out of the question, and offers 480Mbps, but is still limited at around the same as firewire.
No need to replace the Tosiba built in eth sockets, main problem there is you couldn't (if it's built in). PCMCIA is the answer here. PCMCIA (Cardbus etc) gigabit networking card addition, and you don't have to replace the laptops either.