[LordNevar]

This is a way to run 2 copies of D2 without any crashes on the same computer.
You need:
2 CD keys for BNet
1 Hex editor


1. Install D2 with key, patch it fully to 1.11 and enter battle.net.
2. Exit Battle.net again
3. copy your whole D2 install to another directory, eg "c:\games\diablo2a"
3. uninstall d2
4. install d2 with the 2nd key

Now you have 2 installs of D2 on your computer but you can't start a 2nd copy since D2 complains that only one copy can be run at the same time.

1. open d2gfx.dll from c:\games\diablo2a in the hexeditor. I used UltraEdit32 for this.
2. search for the bytes "C0 74 45". in Ultraedit: press ctrl-f and make sure the "find ASCII" is UNCHECKED. enter "C0 74 45".
3. the cursor will jump to offset 84ceh. Change the byte "74" to "EB"
4. save d2gfx.dll again

Now the install with the modified d2gfx.dll can be started while the other one is already running. it will work fine. including the usual "diablo ii.exe -w -ns"

Taken from Kermal13's post on another site.