1 Mac on the network is a pita

Ok - I connected a firewire drive to my mac running 10.3.9 and shared it with evryone using sharepoints. All of the other computers can connect to it without any problem using the apple k command and entering my ip address, logging in as a guest.

One computer on the network - Imac G5 running 10.4.3 (same one that previously had issues) can connect just fine but when he transfers a large file (50 megs) it stops halfway and just hangs up.

Today I had him try and connect to another Mac running 10.4 and it just stalled trying to connect.

Any clue?

Thanks!