To improve gameplay performance, you should set your swap file size to at least 128. Make the minimum and maximum sizes the same. This will prevent Windows from changing it's size during gameplay, the most prevelent cause of hard drive lag in D2. Also, if you can, make the swap file on a hard drive different than the one you installed Diablo 2 on. This will allow your computer to access both at once rather than overloading information going to/from the one with Diablo 2 on it. Finally, if you insist on keeping virtual memory to a minimum, play a game of diablo with the fps info on the top of the screen. (Obtained by typing 'fps' during the game. This is without the quotes.) Take note of how much ram Diablo 2 is using. You can add/remove size from the swap file as needed for however much info your computer is storing on your hard drive.
D/l the latest non-beta drivers for your Geforce from the Nvidia site.
Make sure no unnecessary program(s) is running in the background.