The problem with Vista's new-fangled network stack
All this automatic tuning of the Vista network stack sounds great in theory
But the problem is that some clients don’t support TCP window scaling
Or don’t have it enabled.
Additionally, some firewall products also don’t support it.
If using McAffee uninstall and turn off IPV6
In either scenario, the result is dropped packets, which affects network performance horrendously
Your traffic is literally dropping into a black hole, never to be seen again.
Try this open up an Administrative Command Window
Right-click-Run as Administrator and type in the following command:
netsh interface tcp set global autotuninglevel=disabled
You may also need to type in:
netsh interface tcp set global rss=disabled
The changes take effect straight away, with no reboot needed.
You can also check this site