I finally figured out how to help speed up Windows networking. There was a tip I got from here that I found works REALLY well:
Basically this issue effects more Intel and Broadcom drivers. Almost every machine I see has one of these two network drivers.
In your network card settings, Intel and Broadcom primarily; you need to disable the advanced features.
Receive Side Scaling (RSS Offload)
TCP Offload (IPV4 and IPV6)
IP Checksum Offload
This problem has been around for ages, and was made worse since 2003 SP2 was released.
A couple of good articles:
Fixit packs… wonderful, but this should be included in the critical updates IMHO.