Windows Vista restricts network traffic to 10 packets per millisecond while playing multimedia to prevent skipping. Unfortunately this causes network speed to be pitiful on a gigabit network, especially during file copies over the network.
Service Pack 1 includes a new registry tweak that can be used to change the throttling percentage so you can at least partially fix this problem, but you should be careful to test it out, because you don’t want your audio to skip either.
Note: This setting is only really useful if you are on a gigabit network – the default values should be fine for a Wireless network.
Manual Registry Hack
Open regedit.exe through the start menu search or run box, and then browse down to the following key:
You will see a value on the right-hand side named NetworkThrottlingIndex, which can be changed to anything from 1 to 70 (decimal). I would recommend testing out different values to see what works for you. Note that you’ll need to reboot after making this change.
For more information you can also read the Microsoft KB article on the subject.