>Nothing is using any significant amount of CPU. How is the actual CPU usage when the program is running?
I have written an application that sometimes receives spikes of up to 600 UDP packets/second (several ports). Its running on an old 133MHz Pentium and there is no slowdown at all. How are you using the ethernet. UDP or TCP? For TCP, do you maintain a connection, or establish a new connection for each chunk of data? Do you use datasocket connections or plain TCP? If using Windows, go to a command prompt and type "netstat -an" after runing the program for a while. Is there a buildup of many stale connections. Of course it could also be a hardware conflict, e.g. between the drivers for the NIC and the video card. Have you updated the network card drivers? Maybe try a different NIC or put it in a different PCI slot.
