Not sure what problem you're having - swamping the network, or just plain "this transfer is slower than it should be" or both. First offf, no unicast should swamp the network, kinda by definition. I suppose you could check your interconnect - if it's a "hub" rather than a "switch", then the traffic on any port goes to all ports. I don't know if you can get a hub in this day and age :) but if that's what you have, maybe that's why it's swamping the network. Otherwise, as always, double-check your every single network equipment and configuration. Sometimes, the "router over there" will do something to my "multicast over here". I don't even know why the router got involved (all traffic on the same switch on the same subnet, doesn't need to route) but some stupid oddball setting on the router (and/or the switches in between) got involved. Spanning tree, I'm told, can confuse things sometimes
If the problem is merely "slower than I think it should be", then well - it could still be your network equipment, so always check that. If you have a smart switch, and can set it for "cut-through" rather that "store-and-forward", that would help (a tiny bit.) Check your drivers, and try using theUNDI/Universal driver to see if that changes things. I've often found the Vendor (Dell, Gateway, etc) drivers are pretty bad, and I always go to the manufacturer of the NIC itself (they made it, nobody knows it better!)
For now, since the problem exists in unicast, concentrate on that. It's probably the easiest thing to fix, the fastest to determine what's going on.
Good luck!
PH