[Osiris]

Maybe you have already encountered the strange behavior that it takes much longer to copy large files in Windows Vista than in Windows XP. You thought that the change from XP to Vista would at least be not a disadvantage speed wise but Vista somehow seems to have a problem copying large files. This happens especially with mapped drives but it could also be that you witness network disconnects.
The problem is caused by a new feature called Auto Tuning which is by default enabled in Microsoft Windows Vista. What Auto Tuning does is that it reacts on changes in the network by tuning the receive windows size. The solution would be of course to disable Auto Tuning in Vista. Some users reported that disabling Auto Tuning had a positive effect on their ability to connect to services such as Windows Live Messenger which did not work before.

To disable Auto Tuning and speed up the copy process and avoid timeouts and disconnects do the following:
Open a command prompt and type the following: netsh int tcp set global autotuninglevel=disabled
To turn it on again: netsh int tcp set global autotuninglevel=normal
found this at: One Tip A Day