insert these "codes" in the target line of your Diablo II shortcut. you can find this by right clicking on the icon and selecting properties. then at the very end of the "target" line, add the follow:

-w [for windowed game play]
-nohide [so the window does not minimize]
-res800 [so you don't have to adjust window size]
-skiptobnet [if you want to skip directly to bnet login page]

example:
"C:Program FilesDiablo IIDiablo II.exe" -w -nohide -res800 -skiptobnet
*note
these are only SOME codes. i'm sure there are plenty more.