you right click on your d2 shortcut on your desktop, Select properties, find the line that says Target, at the very end of that line, add -w (put a space after the last character before you add -w).

Ex: "C:\Program Files\Diablo II\Diablo II.exe" -w

on a side note, you can add other targets to mess around with.

-ns causes d2 to have no sound so you can listen to music
-skiptobnet lets you skip right into the battle.net log in screen.

theres more, i can link you later if you want.