I have used DOSBox to play via IPX, modem emulation, and null-modem emulation over the net to the other side of the country and not had a bit of problem with it. I'd check the system in question. Maybe it is running in half-duplex or something.

cycles might be configured badly

True. For the games you mentioned, you can use a dynamic core with cycles set to max for the best performance on any machine. That is how I run those games, and they run flawlessly with those settings.

thanks everyone for your responses

I was using max cycles and auto core settings

I'll look into the duplex thing (once i figure it out...)

Thanks again

The automatic core fails miserably for most of my needs. Try a dynamic core with max cycles. I have the most success with that, and I can tell you that Duke3D, Doom, and WC2 run wonderfully on the dynamic core.