I have found that the best modification to make is to add an entry in the registry that creates a receive window size of 64240. Others recommend that you change a whole host of other settings but I believe these to be largely questionable, and at the worst - a hard to undo operation. 

To install this modification, Right-Click on this file WindowsNT2000XP-64240 RWIN.reg and select 'Merge' and you will be asked if your are sure you want to install this information in the registry. Select 'Yes'  and than re-boot your system at your convenience.

This file adds the TcpWindowSize entry to the registry and sets a value of 64240. It also adds the Tcp1323Opts entry and sets it to 0. Neither of these entries exist in the unmodified operating system.

To return your Windows NT computer back to the original settings Save This File to your disk and than right-click on it and select install. This will remove both of the entries and it will be as if you never changed it - once you've re-booted your machine.

For a Microsoft Whitepaper (in Word format) on the TCP/IP stack in Windows NT 3.x see this link Microsoft Windows NT 3.5/3.51/4.0: TCP/IP Implementation Details TCP/IP Protocol Stack and Services, Version 2.0

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