I once had a Netgear NIC on a desktop machine that behaved in a similarly slow fashion. It wasn't what was running on the PC, it was the card (or its driver). I replaced the card with a different brand and all was well.

I suppose these NICs are built in on your laptops correct? If so, it would probably take some doing to get at the mini-PCI or whatever card format they use to try replacing it.

Stu