Ok, this may be a bit difficult to explain, 'specially with the lack of details (and knowledge) I have so please bear with me...... :-}
I have a small network consisting of ~50 machines split over five rooms and connected using combinations of unmanaged (Netgear) switches and hubs, ethernet and fibre. For simplicity, I'll call the rooms A,B,C,D & E.
In room A there is an application that when running, periodically broadcasts 5s updates to the rest of the network. This is not particularly bandwidth intensive (maybe 100kb at peak) and simple network monitoring using netassyst shows little utilisation etc.
Without this application running, I get good ping times (