Windows Vista has optimized the network speed by default. However there are a lot of installed network items in Vista Network Properties dialog:
You can add some Network speed to your connection by disabling some unusing network items. You can absolutely safe disable:
QoS Packet Scheduler - this item is in no use in most home environments.
Internet Protocol Version 6 (TCP/IPv6) - protocol of the future. If your PC is not inside of Network of Future - disable it.
File and Printer Sharing for Microsoft Networks - if you have not shared files or printers in network - disable it.
Link-Layer Topology - Allows Vista computers to be seen from the other Vista computers in the Network Map.
Recommended settings (if you have not shared files and folders and you are not inside of IP6 network):
Also you can add some network speed using WinTools.net tweaks.
Go to Net Tweak tool.
Press Use optimum settings for selected configuration.
Select suitable importance for your connection, for example: LAN, Cable Modem, xDSL, ISDN, T1, etc.
And press Apply button.
Note: You can restore your network setting using the option MS Windows default Internet and Network configuration.