This is not recommended practice but might work - there's a new feature in Vista called TCP Auto-tuning which can sometimes affect internet connectivity.
Go to start orb/search bar, type
right click on Command Prompt and select Run As Administrator.
In the command prompt window type;
netsh interface tcp set global autotuninglevel=disabled
You may need to reboot to see if the connection is any better. Disabling the feature entirely can affect other services, you can also try LOW or HIGH in place of Disabled.
More reading here; click here