If you use Vista and you just want a shortcut icon to turn ON/OFF your network you can do this :
Click
Start, Select
Network, Select
Network and Sharing Center, Under TASK select
Manage Network Connections, you will see an icon for your Network connection, all you have to do is either "Drag and drop that icon onto your desktop" or "Right Click over the icon and select to create the shortcut, it want allow you to create the same shortcut there so it ask to add it to the desktop, just select yes.
When you double click on that icon on your desktop it will give you the menu with the selection "Disable" to disable your network. When you want to turn your network back on just click on the short cut you created again to enable it.
You can also drag that Short Cut Icon to the quick launch bar on the bottom left if you just want to single click it instead of having to double click it on the desktop.
"If you ever have any problems, which I never have had, you can always Start/Network/Network and Sharing Center and select Diagnose and Repair", or just right click and select Diagnose and repair on the network connection icon on the bottom right of your screen "The two monitors symbol".
You can also just click on the Shortcut Icon you created and run diagnose from there.
You can probably do this in XP or Windows 7 in a similar way, I haven't used XP in a while so I can't remember the menu selections, I would think Windows 7 would be similiar to Vista, I've only used their Beta version of 7 and that's been a while back so I can't remember.
If your computer has a lot of memory and processor power you may not even need to turn off the network connection or see any difference in performance. A lot of this stuff has to do with automation IMO, I have my computer take care of things at a time when I don't use it, so there's very little accessing my connection, and when it's done it turns itself off.
Bobby