Not sure if this may help.
Thanks to Jim_F for this ,which was a reply to another thread.
If you try this,i would create a restore point first.
Also you should double check your router settings against your ISP settings first.
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 do but don’t have it enabled. Additionally, some firewall products also don’t support it. 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.
So if you’re experiencing excessive network lags on your Vista machine, especially compared to non-Vista machines, it might be worthwhile disabling auto-tuning. Do this by opening 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. Bear in mind that this is a global change, so it may really be worth your while to sit down and nut through your network's QoS settings to get things running happily without disabling auto-tuning.