Hardware setup: network speed and raid... working from a server

hey guys

some friends of mine are working together on three Mac Pros connected to a G5 computer. the g5 functions as a server and has 3 hard drives via firewire attached. now the three are often transferring gigabytes of data from and to the server. the speed is horrible and this is just no solution for the future... but what woud be a better solution? something like an upgrade of the current setup that doesn't cost too much...

i told them they should get a PCI-X card like this one (the g5 is quite old so it doesn't support pcie yet). i thought best would be to then set up a raid5 system to speed up the connection!
but i think the external hard drives are probably not the only bottleneck of their setup.

is there a way to speed up the lan speed? does it make more sense to have all 3 computers connected individually to the server? do you guys think the g5 could be to old to function as a good server?

thanks for any help

Not really a mac-forum here so that's probably why no one has responded.
I would say the external drives are the main source of slowness you are seeing.
You have Gigabit between all computers so your fine there.
I don't know enough about Macs to say anything about the G5.

How long does it take to transfer a large file from one computer to another? Is is faster than transferring the same file to the server? The Gigabit LAN shouldn't be the bottleneck. How fast is Firewire on that system and do all hard disks share the same bus? Is a large file transfer on the server itself fast?