Another new member of the team. Barry owns his own 'broadband for businesses' consultancy company, and has plenty of rich experience to share with us! Go Barry!! 
Note:
Please note that you can cause damage to your system if you make a wrong move when editing the Windows Registry, so you do so at your own risk. Back up your registry before attempting to use any of the registry tweaks.
Windows NT is designed for networks, so you probably won't notice a massive increase in performance levels after using any of these tweaks. However, is the NT equivalent of the DefaultRcvWindow is called the TcpWindowSize.
The TcpWindowSize, (known as DefaultRcvWindow in other Windows versions) is a buffer that fills with data determining how much of that data the receiving computer will receive. If the size of the TcpWindowSize is set incorrectly, then the speed of that Internet connection can be affected. The TcpWindowSize can be specified within the Microsoft Windows Registry to maximise the performance of an Internet connection.
Ok let's get started:
Step 1: Open up the Windows Registry Editor. To do this click on the Windows Start button, click on "Run" and type in "regedit" before clicking "OK".
Step 2: Find the following registry key: HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\Tcpip\Parameters
Step 3: Look for a DWORD value named "TcpWindowSize". If you don't have this then you will have to create it (see screenshot):
Step 3: Once you have located or created "TcpWindowSize", you need to set the value of this. Set the value to
"64240" (without quotes).
Step 4: Close the registry editor and restart your computer.
Didn't this go smoothly for you? Try consulting our community in the talkbroadband.com forums!