if you are having either of these issues you can try to disable a new function in Windows Vista/Win7/2008 called auto-tuning.
Auto-Tuning allows the operating system to continually monitor the routing conditions (bandwidth, network delay, application delay) and configure connections (scale the TCP Receiving Window) so as to maximize the network performance.
However, I’ve found that certain NICs,switches, and routers do not understand this new protocol and it ends up slowing things down quite a bit.
You can find information on how to disable this feature here:
There is an automatic “fix it” download that you can run there if needed.